Humane methods of pig management and systems for facilitating said methods

Abstract

The invention relates to humane methods of managing feral and domestic (e.g. farmed) pig populations. In particular, the methods involve humane culling of pig populations with the use of a chemical toxicant composition and systems for facilitating said methods. The present invention is particularly suitable for humanely de-populating domestic pigs, for example, where there is a disease outbreak within a piggery.

Description

[0001] Humane Methods of Pig Management and Systems for Facilitating said Methods

[0002] Field

[0003] The present invention relates to humane methods of managing feral and domestic (e.g. farmed) pig populations. In particular, the methods disclosed herein involve humane culling of pig populations with the use of a chemical toxicant composition and systems for facilitating said methods. The present invention is particularly suitable for humanely depopulating domestic pigs, for example, where there is a disease outbreak within a piggery.

[0004] Background

[0005] Feral pigs cause environmental, biodiversity, and agricultural damage and pose a risk for the spread of diseases that can be on a large geographical scale, so feral pigs have direct impact on the environment, agricultural production, rural industries and semi urban amenity.

[0006] In Australia, feral pigs are estimated to number in excess of 4 million with some estimates as high as 25 million. Feral pigs occupy some 40% of the land mass of Australia and can breed rapidly in favourable conditions. These population estimates mean that at times of peak abundance there may be more feral pigs in Australia than grazed cattle. Feral pigs inhabit, and are well adapted to a wide range of habitats that include sub-alpine, temperate, sub-tropical, and tropical zones, and they are present in most Australian states and territories.

[0007] Furthermore, in the United States, the presence of some 8-12 million feral pigs (also referred to as hogs, boar, or swine) has been reported in some 34 states ranging from California to Virginia, the majority residing in Texas and other southern states including Louisiana, Mississippi, and Florida. Feral pigs are the most abundant introduced ungulate in the United States and their density within ranges and range areas are expanding rapidly.

[0008] Feral pigs have a very high fecundity and frequently raise litters in excess of 6 piglets per breeding sow. Thus, the capacity for feral pig populations to respond to control measures or to totally exploit a food supply and to cause environmental damage and predation is great, so large-scale and sustained control measures to lower populations are needed. Feral pigs adversely impact agricultural production, environments and ecosystems. A number of studies have identified a range of environmental and agricultural problems arising from feral pig infestations (Alexiou (1984) Effects of feral pigs (Sus scrofa) on sub-alpine vegetation at Smokers Gap, ACT, Proceedings of Ecological Society of Australia, 12: 135- 142; Tisdell, C. A., (1982) Wild Pigs: Environmental Pest or Economic Resource? Pergamon Press, Sydney; Miller, B. and Mullette, K., (1985) Rehabilitation of an endangered Australian bird: the Lord Howe Island Woodhen, Tricholimnas sybveslris. Biological Conservation, 34: 55-95; Mitchell, J. and Mayer, R., (1997). Digging by feral pigs in the wet tropics world heritage area of north Queensland, Wildlife Research, 24: 591-601; Choquenot, D., McIlroy, J. and Korn, T., (1996) Managing Vertebrate Pests: Feral Pigs (Ed. M. Bomford) Bureau of Resource Sciences, Australian Government Publishing Service, Canberra 163 pp; Mitchell, J., (2000) Ecology and management of feral pigs in tropical rainforest, Unpublished PhD Thesis, James Cook University of North Queensland, Townsville; Hone, J., (2002) Feral pigs in Namadgi National Park: dynamics, impacts and management, Biological Conservation 105: 231-242); Singer, F. J., Swank, W. T., and Clebsch, E. E. C., Effects of wild pig rooting in a deciduous forest., Wildlife Management 48: 464-473; Lacki, M. J., and Lancin, R. A., (1986) Effects of wild pigs on beech growth in Great Smoky Mountains National Park, Journal of Wildlife Management 50: 655-659. The key points from these various studies are summarised below.

[0009] The predatory behaviour of feral pigs causes major economic damage for animal production enterprises over wide areas. The damage is so severe that some areas cannot sustain productive grazing of livestock, such as sheep, due solely to the widespread infestation of feral pigs. The species’ impact on agricultural production in Australia has been conservatively estimated to be in excess of 100 million Australian dollars annually.

[0010] Feral pigs also cause significant damage to the environment due to their destructive foraging habits which include digging for plant roots or soil fauna including worms (rooting) and consumption of plants and plant root systems. This destructive behaviour, and their need to access areas of food resource or water wallowing points, can damage infrastructure including fencing, dams and levy banks and also causes damage wide areas of fragile riparian habitat. Feral pig fecal contamination of waterways and water storages is also a concern. Their effect on native animal species is unknown but is likely to be severe in view of their predatory behaviour and competition for food resources. Feral pigs are known to aggressively predate new born lambs to such an extent that profitable sheep farming has been discontinued in large areas as a result of the incursion of feral pigs into these areas. It is likely also that feral pigs adversely impact on native wildlife species though these impacts are not well quantified.

[0011] Apart from direct damage to grazing enterprises and the environment, feral pigs also harbour several major human and animal diseases. Many diseases are zoonotic and the pig provides an ideal amplifying host. Japanese encephalitis virus, leptospirosis, brucellosis and melioidosis have already been detected in feral pigs in Australia. However, an even greater risk comes if there is an incursion of foot and mouth disease (FMD) virus into the feral pig population, where the cloven hoofed pigs provide an amplifying host and virus carrier that is widely distributed and highly mobile.

[0012] In the United States, pseudorabies virus (PRV) has been eradicated from domestic pigs however PRV continues to circulate in feral pig and raccoon populations. Accordingly, feral omnivore populations can also be a reservoir for fresh PRV outbreaks.

[0013] More recent findings under experimental conditions have linked the potential transmission of Ebola viruses in non-human primates to contact with caged pigs which have been reported in laboratory trials to carry the virus in lesions focussed in the lungs without a lethal outcome for the pig.

[0014] Details of the environmental, human health, animal health and agricultural production problems that arise already, or which might arise, from an unchecked expansion in feral pig numbers are provided in the book “Managing Vertebrate Pests: Feral Pigs” (Choquenot, D., McIlroy, J. and Korn, T., (1996) Managing Vertebrate Pests: Feral Pigs (Ed. M. Bomford) Bureau of Resource Sciences, Australian Government Publishing Service, Canberra 163 pp. Infestation of other omnivorous species such as raccoons, collared peccaries, opossums, possums and rodents with viruses or other pathogens known in pigs can give rise to similar adverse agricultural, environmental, financial and health concerns in various countries. The recent spread of African Swine Fever (ASF) virus in feral pig populations from Russia through Asia and Western Europe, also now poses a considerable threat to farmed pig populations globally. This highly lethal and untreatable disease has caused the urgent destruction of some 250million farmed pigs in China alone. Once a farm piggery is infected with ASF the only approved action is to rapidly cull all of the pigs to prevent disease spread. There is therefore a considerable effort focussed on a reduction of the risks posed by feral omnivorous species in Australia, United States, New Zealand, Europe and South America and other parts of the world which have unchecked populations of such species.

[0015] Despite their impact, the control of omnivores such as feral pigs, is generally timeconsuming, ad-hoc and reactive rather than pro-active management. Many techniques are currently employed for mainly localized control. The methods include baiting with poison baits, shooting (with ground teams or by helicopter or fixed wing based marksmen), trapping (for destruction or harvesting), and fencing (to attempt to exclude pigs from an area). It is recognized that, while no single technique can be expected to be 100% effective in all situations, the broad-scale and integrated baiting campaigns are most cost-effective for reducing and maintaining feral omnivore populations at low densities across large areas. Typical baiting campaigns include ground baiting after pigs are clustered to a site of habitual feeding or aerial baiting where the bait is dropped from an aircraft into the loci of the target omnivore population to be controlled.

[0016] Lethal baiting campaigns include the use of various poisons, for instance, sodium fluoroacetate (1080) which is placed in or deposited on cereal grains, fermented grain, compressed bran / pollard pellet baits, fresh or dried meat, offal, carcasses, lupin seeds, and fruit and vegetables and in manufactured baits. Of these, the use of soaked or dry wheat grain or fresh meat baits are the most common. Feral pigs have also been baited under experimental conditions with warfarin soaked into grain or by applying yellow phosphorus suspended in carbon bisulphide onto carcass offal that is scavenged by the pigs. The use of yellow phosphorus as a poison is allowed only under permit in one state of Australia and is banned in other jurisdictions, as it is not targeted or humane. Likewise, the use of warfarin to trigger haemorrhage in dosed pigs is not considered humane and has not been approved in Australia. The use of sodium fluoroacetate is effective but requires high doses of the toxin as pigs are relatively less susceptible to this toxin than certain other pest species such as foxes, wild dogs, rabbits and feral cats. Since large quantities of sodium fluoroacetate poison are required to kill pigs than are needed for more susceptible species such as wild dogs and foxes and rabbit, this high doing requirement poses a risk to other species that may take some bait materials such as meat and grain that are attractive to these potential non-target species. Manufactured pig baits pose lower risk of non-target uptake due to their demonstrated target specificity and lack of attractiveness to certain non-target species. Of the various control means discussed above, poison baiting of feral pigs and other omnivore populations is recognised as one of the most effective means of controlling such populations and reducing the damage they cause. Unfortunately, however, two of the main problems with many of the bait types made from grains or meat and carcass offal or pellets is that they require high dose levels of toxicants and that they exhibit poor target specificity.

[0017] Accordingly, while the commonly employed baiting campaigns may prove effective in controlling feral omnivore (e.g. pig) numbers in a particular area, such campaigns may also pose a risk to or adversely affect individuals of other species of animals which may be desired or native.

[0018] Other disadvantages of the present baiting regime can be attributed directly to the specific poison used. For instance, a disadvantage of 1080 is that feral pigs appear to be relatively resistant to the effects of the poison compared to rabbits, foxes, and wild dogs for which it is a more ideal poison. For example, during captive trials with bait delivered 1080, (McIlroy et al, Australian Wildlife Research 16: 195-202) wild dogs required 0.1 Img / kg to receive an LD50 dose whereas feral pigs were reported to require at least Img / kg and some as high as up to 4.11 mg / kg (O'Brien et al, Australian Wildlife Research 15: 285-291) this being up to a 40 fold multiple of the dose rate used for canid pests. Moreover, pigs may weigh more than 100kg compared to 5-20kg bodyweight for foxes and wild dogs. Thus the dose of 1080 for control of feral pig is very large.

[0019] While the terminal toxic events associated with 1080 toxicosis involve enzyme inhibition within mitochondria are not thought to be accompanied by conscious pain, the effects of blockade of energy producing enzymes of the Tri Carboxylic Acid (TCA) Cycle can raise blood citrate levels which then reduce free calcium that is necessary for muscle coordination. As a consequence there are disturbances in nervous control of muscle function due, it is thought, to accumulation of citrate in blood and its ability to chelate and remove extracellular calcium ions (hypocalcaemia), thus effects on behaviour that can appear unpleasant to the untrained observer. Humans that have recovered from nearly lethal exposures to 1080 have not recalled pain after the event however the final phases of toxicosis have been likened to hypoglycaemic or epileptic fitting. Similarly humans accidentally exposed to over doses of citrate as an anticlotting agent in blood transfusion, exhibit similar painless spasm associated with the induced hypocalcaemia. Apart from the limitation of high required dosing, sodium fluoroacetate is a naturally occurring plant toxin in some Australia plant species and this leads to partial evolutionary tolerance for many native herbivore species in Australia. For this reason and others, 1080 remains presently a common toxin choices for feral pig management in Australia. This chemical is not available for pig control in the USA or elsewhere in the world. Nevertheless, the high doses of sodium fluoroacetate that are required to get reliable lethal control of feral pigs mean that this is not a perfectly suitable toxin for pig management especially since such high doses may put potential non-target species at risk. This toxin can take up to 12 hours for pigs to die and so carcasses are often at some distance from baiting points and scattered. This is an impediment to use of this toxin in a disease control situation where carcass recovery is necessary to prevent infection spread. This risk to non-target species is particularly high when substrates such as grain and fresh carcass meat are used as bait carriers since some non-target animals show a preference for these substrates and the removal of baits by non-target species can reduce the bait available for the feral pig target animals, making some baiting programs more expensive and less effective.

[0020] People poisoned with other toxins such as phosphorus (CSSP) or strychnine have reported substantial pain and suffering and it is highly likely that such poisons are too inhumane to be used to control feral animals such as a pig. Similarly, while warfarin is used therapeutically in low doses for humans suffering from blood clotting disorders and this use is not associated with pain, provided that no uncontrolled haemorrhage is induced. However, the use of this anticoagulant in large animals such as feral pigs, which are susceptible to this anticoagulant, may give rise to delayed effects, painful haemorrhaging and swelling in sensitive tissues and protracted suffering in some animals and therefore it is also not a preferred poison for this application.

[0021] In addition to feral pig species there is also a need from time to time to humanely euthanize populations of domestic pigs, for example, where there is a disease outbreak within a piggery. For instance, African swine fever (ASF) is a contagious viral disease of both domestic and feral (wild) pigs. Currently, there is no vaccine. ASF kills about 80 % of the pigs it infects. In the acute form of the disease is caused by highly virulent strains, where pigs develop a high fever, but show no other noticeable symptoms for the first few days They then gradually lose their appetites and become depressed. In white-skinned pigs, the extremities turn blueish-purple and haemorrhages become apparent on the ears and abdomen. Groups of infected pigs lie huddled together shivering, breathing abnormally, and sometimes coughing. If forced to stand, they appear unsteady on their legs. Within a few days of infection, they suffer extensive haemorrhaging, enter a comatose state and then die. In pregnant sows, spontaneous abortions occur.

[0022] In milder infections, affected pigs lose weight, become thin, and develop signs of pneumonia, skin ulcers, and swollen joints.

[0023] The clinical symptoms of ASFV infection are very similar to classical swine fever, and the two diseases normally have to be distinguished by laboratory diagnosis.

[0024] The virus can be spread by ticks, and possibly other biting insects but also by swine eating pork products that contain the virus or via exposure to contaminated areas such as pig pens. The National Pig Association, a UK industry body, states that the virus can also be transmitted by direct or indirect contact with infected pigs, faeces or body fluids. As the virus may survive 11 days in pig faeces, and months or years in pork products or for extended periods in pig carcasses, the Association advises strict biosecurity measures for pig farms including a three-day quarantine on entering the UK, and avoiding both pigs and areas where wild boar are found.

[0025] Thus, in pig farming practice the risk of exotic viral diseases such as foot-and-mouth disease (FMD), African swine fever (ASF) and Classical swine fever (CSF) is ever present. These diseases are very effectively spread through feeding to pigs infected or contaminated meat or meat products which may be imported from a country where the diseases are present.

[0026] If a commercial piggery becomes infected with these virulent and fatal exotic diseases, the preferred method to reduce contagious spread is to quickly kill and burn or bury all of the pigs in the affected facility. In large commercial operations this may mean the urgent killing of tens or even hundreds of thousands of farmed animals.

[0027] One of the most common ways of euthanizing populations of infected pigs is with the use of captive bolt guns. These devices fire a restrained steel bolt through the skull to quickly kill the animal. While fast and effective it can cause distress to pigs and also to operators, and poses problems for removal of carcasses from pens. Moreover, the blood produced from this process may exacerbate contamination of piggeries and increase the spread of infection.

[0028] Nitrite salts have been recently reported to be potentially suitable for the control of pig populations (sus scrofa) and other omnivorous animals such as pest brush tail possums (Trichosurus vulpecula) in New Zealand. Sodium nitrite in particular is commonly approved and used at very low doses for the preservation of many foods where it reduces the risk of bacterial contamination and improves the colour of certain meat products. While the use at low doses as a food preservative poses low risk, in high doses it causes the conversion of normal haemoglobin to methaemoglobin by acting as a direct oxidiser of the iron molecule in the haem protein, Since methaemoglobin is unable to effectively transport oxygen to the brain and other tissues, an animal that achieves blood levels of methaemoglobin above approximately 70% of all haemoglobin suffers from an acute metabolic anoxaemia and will become unconscious and die. The clinical effect of methaemoglobineamia is similar to the effects of carbon monoxide gas that binds strongly to normal haemoglobin to also prevent oxygen transport to essential organs and the brain. The effect of nitrite induced methemoglobinaemia in preventing oxygen transport and is therefore more humane and faster than the actions of most if not all other poisons. Moreover, relative to other animals, the pig (also known as swine or hog) has a deficiency of the enzyme methaemoglobin reductase that converts methaemoglobin back to normal haemoglobin, is present at higher levels in many other animals that in pigs. This enzyme acts to protect most animals from the accumulation of low to moderate levels of methaemoglobin that can arise naturally with exposure to any oxidising compound such as even nitrite present in some foods and water. The pig is thus especially susceptible to this type of poison as it has a deficiency in the means to reverse the poisoning process of methaemoglobin formation.

[0029] Despite its effectiveness as a toxicant, sodium nitrite is an unstable molecule that can oxidise and which can react also with other chemicals that are present in foods. Sodium nitrite is highly hygroscopic and will dissolve in water readily and then, after dissolution of atmospheric carbon dioxide in the water to form carbonic acid, will undergo a series of breakdown reactions. Nitrites are highly polar and may even obtain acid (H+) by deprotonation of water molecule to generate a highly alkaline initial solution. The number of potential degradation pathways for interaction with other components of a bait comprising sodium nitrite are large but one breakdown product is nitric oxide gas (NO). Nitric oxide gas is itself unstable but which can act as a corrosive agent, a chemical messenger and a vasodilator, and which may oxidise exothermically in air to nitrogen dioxide gas (NO2). Nitrogen dioxide may be converted to nitrous acid (HNO2) which can then combine with itself to generate more nitrous acid and water and also ultimately nitric acid. (HNO3). Sodium nitrite can also oxidise to sodium nitrate. These reactions, including the natural formation of nitrate as part of the soil nitrogen cycle, provide for ultimate degradation of nitrite in the environment. This lack of persistence and total degradation is a valuable feature from an environmental perspective but this instability is problematical when seeking to use the nitrite salts in bait formulations. Not only do the degradation products cause chemical reactions within the bait but the direct breakdown products are all noxious to mucous membranes such as in the sensitive pig nose. Sodium nitrite is also salty tasting and pigs are generally aversive to high salt diets. Thus, the use of sodium nitrite or other nitrite salts as a toxin in large amounts in bait products poses formulation challenges to achieve a bait that is stable during storage and use but at the same time is able to deliver larger quantities of the toxicant to the pig in a bait that remains palatable to the pig.

[0030] Accordingly, an improved method is required to protect the sodium nitrite in the bait carrier system to achieve stability of the formulation over extended shelf-lives by, in part, reducing the production of noxious or aversive breakdown products which is thought to diminish the effectiveness of the bait. If such stability can be achieved this would in turn reduce the possibility of the target pig detecting the nitrite and lead to an increase in voluntary uptake.

[0031] Any new variation of a bait formulation will still need to also provide effective release of the nitrite into the animal to induce high levels of methaemoglobinaemia and thus cause a quick and painless death without suffering.

[0032] The present invention serves to address these long-term stability and voluntary palatability shortcomings which currently exist in the art while at the same time providing an effective bait formulation which serves to humanely control feral omnivorous pest populations and domestic farmed pigs which may be susceptible to an exotic disease such as Foot and Mouth Disease (FMD) and African Swine Fever (ASF). Therefore in preparedness for an incursion, the domestic pig industry seeks to have proven methods to humanely and quickly depopulate large numbers of pigs if required should an outbreak be identified.

[0033] Thus the present invention also serves this currently existing shortcoming.

[0034] Summary of Invention

[0035] The present invention has been driven by the necessity to improve the delivery form of sodium nitrite as a toxicant in pest bait formulations. The present inventors have found that the use of specific nitrite encapsulation ingredients in conjunction with specific dry formulation feed ingredients provides an unexpected significant improvement in terms of ease of use, stability, palatability and toxicity compared to other combinations which use combinations with feed ingredients, with for instance, moisture content above about 10-15% or where the nitrite is presented as a paste material. Encapsulation coverage minimises the propensity of nitrite leaching due to edge effects which are greatly minimised within the final bait formulation.

[0036] In one aspect the invention provides a method of humanely de-populating a population of pigs including the step of providing to said population of pigs a dry mix composition comprising microencapsulated sodium nitrite microspheres and one or more dry palatable carrier ingredient.

[0037] In one embodiment the pig population is a feral pig population.

[0038] In one embodiment the pig population is a domestic (or farmed) pig population.

[0039] In one embodiment the pig population is a domestic pig population which has been exposed to or is suspected to have been exposed to a contagious disease.

[0040] In certain embodiments the one or more dry palatable carrier ingredient is selected from grain (eg wheat, corn (including ground corn like semolina and polenta), sorghum, millet, barley, rye, quinoa, and buckwheat), and peanuts.

[0041] In one embodiment the pig population is a domestic pig population which has been exposed to or is suspected to have been exposed to a contagious disease, selected from Foot and Mouth Disease (FMD), African Swine Fever (ASF), classic swine fever (CSF), Influenza A virus, Pseudorabies, Japanese Encephaitis Virus or Swine Brucellosis.

[0042] In other embodiments the microencapsulated sodium nitrite is encapsulated with lipids, acrylic polymers, glycerides, fatty acids and alcohols, paraffin and mixtures thereof.

[0043] In certain embodiments the coating material for nitrite salts can be realised using ethyl cellulose (EC) and linoleic acid (LA) as a plasticizer in an amount from about 99: 1 to about 99.99: 0.01 as a % weight to weight ratio (EC : LA).

[0044] In certain embodiments the coating material for nitrite salts can be realised using zein protein and PVP in an amount from about 95:5 to about 99.5:0.5 as a % weight to weight ratio.

[0045] Accordingly, in an aspect the invention provides a method of humanely de-populating a population of pigs including the step of providing to said population of pigs a dry mix composition comprising microencapsulated sodium nitrite microspheres and one or more dry palatable carrier ingredient, wherein the microencapsulated sodium nitrite microspheres are encapsulated by a coating material comprising ethyl cellulose / linoleic acid (EC / LA) microencapsulated sodium nitrite microspheres, wherein the ratio range of ethyl cellulose to linoleic acid is in an amount from about 99: 1 to about 99.99: 0.01 as a % weight to weight ratio.

[0046] Accordingly, in an aspect the invention provides a method of humanely de-populating a population of pigs including the step of providing to said population of pigs a dry mix composition comprising microencapsulated sodium nitrite microspheres and one or more dry palatable carrier ingredient, wherein the microencapsulated sodium nitrite microspheres are encapsulated by a coating material comprising zein protein and PVP in an amount from about 95:5 to about 99.5:0.5 as a % weight to weight ratio.

[0047] It will be appreciated that the term "de-population" is synonymous with culling and the present process presents a de-population methodology which uses sodium nitrite to humanely euthanize one or more pigs in a given pig population.

[0048] In an embodiment and with reference to the above aspect the method may be applied to a pig population which has been exposed to or infected with pathogens which pose a clinically serious risk or lethal risk to the pig population or may be passed from pigs to humans. For instance, in an embodiment the toxic feed composition may be used for euthanizing pig a population which has been exposed to or infected with African Swine Fever (ASF).

[0049] In an embodiment the ethyl cellulose / linoleic acid coating material is added to the nitrite salt to form the microspheres at from about 2.5 to 30% weight to weight based on ethyl cellulose / linoleic acid to nitrite salt. Preferably the nitrite salt is in granular form.

[0050] In an embodiment the zein protein / PVP coating material is added to the nitrite salt to form the microspheres at from about 3.5 to 20% weight to weight based on zein protein / PVP to nitrite salt.

[0051] Therefore, in another aspect the invention provides a method of humanely de-populating a population of pigs including the step of providing to said population of pigs a dry mix composition comprising microencapsulated sodium nitrite microspheres and one or more dry palatable carrier ingredient, wherein the microencapsulated sodium nitrite microspheres are encapsulated by a coating material comprising ethyl cellulose / linoleic acid (EC / LA) microencapsulated sodium nitrite microspheres, wherein the ratio range of ethyl cellulose to linoleic acid is in an amount from about 99: 1 to about 99.99: 0.01 as a % weight to weight ratio and the ethyl cellulose / linoleic acid coating material is added to the nitrite salt to form the microspheres at from about 2.5 to 30% weight to weight based on ethyl cellulose / linoleic acid to nitrite salt. In a further aspect the invention provides a method of humanely de-populating a population of pigs including the step of providing to said population of pigs a dry mix composition comprising microencapsulated sodium nitrite microspheres and one or more dry palatable carrier ingredient, wherein the microencapsulated sodium nitrite microspheres are encapsulated by a coating material comprising zein protein and PVP in an amount from about 95:5 to about 99.5:0.5 as a % weight to weight ratio, wherein the zein protein / PVP coating material is added to the nitrite salt to form the microspheres at from about 3.5 to 20% weight to weight based on zein protein / PVP to nitrite salt.

[0052] In certain embodiments the pig population ingests an average dose of the toxic dry mix composition at a rate of about 20-60g sodium nitrite / pig (based on a 50kg pig size) or about 500-900mg of sodium nitrite / kg of pig representing a certain overdose for quick effect. For such pigs it is possible to achieve 100% deaths within a mean of 2 hours of ingestion.

[0053] In a preferred embodiment the sodium nitrite comprises from about 5-15 wt / wt% of the toxic dry mix composition

[0054] Therefore, in another aspect the invention provides a method of humanely de-populating a population of pigs including the step of providing to said population of pigs a dry mix composition comprising microencapsulated sodium nitrite microspheres and one or more dry palatable carrier ingredient, wherein the microencapsulated sodium nitrite microspheres are encapsulated by a coating material comprising ethyl cellulose / linoleic acid (EC / LA) microencapsulated sodium nitrite microspheres, wherein the ratio range of ethyl cellulose to linoleic acid is in an amount from about 99: 1 to about 99.99: 0.01 as a % weight to weight ratio and the ethyl cellulose / linoleic acid coating material is added to the nitrite salt to form the microspheres at from about 2.5 to 30% weight to weight based on ethyl cellulose / linoleic acid to nitrite salt, wherein the dry mix composition is provided at a rate of 20g-60g sodium nitrite / pig (based on a 50kg pig size) or approximately 500-900mg sodium nitrite / kg, and wherein the sodium nitrite comprises from about 5-15 wt / wt% of the dry mix composition. In a further aspect the invention provides a method of humanely de-populating a population of pigs including the step of providing to said population of pigs a dry mix composition comprising microencapsulated sodium nitrite microspheres and one or more dry palatable carrier ingredient, wherein the microencapsulated sodium nitrite microspheres are encapsulated by a coating material comprising zein protein and PVP in an amount from about 95:5 to about 99.5:0.5 as a % weight to weight ratio, wherein the zein protein / PVP coating material is added to the nitrite salt to form the microspheres at from about 3.5 to 20% weight to weight based on zein protein / PVP to nitrite salt, wherein the dry mix composition is provided at a rate of 20g-60g of sodium nitrite / pig (based on a 50kg pig size) or approximately 500-900mg of sodium nitrite / kg, and wherein the sodium nitrite comprises from about 5-15 wt / wt% of the dry mix composition.

[0055] In certain embodiments the inventors have demonstrated additional stability improvement by incorporating a pH stabiliser into the dry palatable carrier ingredient, to afford a pH to the bait of greater than pH 7. In an embodiment calcium carbonate can be added to the dry mix composition mater to get the pH >7 as it was found that sodium nitrite in the dry mix composition may be unstable at pH <7. Lime can also be used as a pH modifier but so could certain buffers.

[0056] Therefore, in another aspect the invention provides a method of humanely de-populating a population of pigs including the step of providing to said population of pigs a dry mix composition comprising microencapsulated sodium nitrite microspheres and one or more dry palatable carrier ingredient, wherein the microencapsulated sodium nitrite microspheres are encapsulated by a coating material comprising ethyl cellulose / linoleic acid (EC / LA) microencapsulated sodium nitrite microspheres, wherein the ratio range of ethyl cellulose to linoleic acid is in an amount from about 99: 1 to about 99.99: 0.01 as a % weight to weight ratio and the ethyl cellulose / linoleic acid coating material is added to the nitrite salt to form the microspheres at from about 2.5 to 30% weight to weight based on ethyl cellulose / linoleic acid to nitrite salt, and wherein the dry mix composition is characterised with a pH>7. In a further aspect the invention provides a method of humanely de-populating a population of pigs including the step of providing to said population of pigs a dry mix composition comprising microencapsulated sodium nitrite microspheres and one or more dry palatable carrier ingredient, wherein the microencapsulated sodium nitrite microspheres are encapsulated by a coating material comprising zein protein and PVP in an amount from about 95:5 to about 99.5:0.5 as a % weight to weight ratio, wherein the zein protein / PVP coating material is added to the nitrite salt to form the microspheres at from about 3.5 to 20% weight to weight based on zein protein / PVP to nitrite salt, and wherein the dry mix composition is characterised with a pH>7.

[0057] The invention also provides a method for humanely controlling a feral pig population, including the step of dispersing within the area of foraging of said feral pig population a dry mix composition as disclosed herein.

[0058] The invention also provides a method for humanely controlling pig populations, in particular farmed or domestic pigs, including the step of dispersing within the pen of said farmed pigs a dry mix composition as disclosed herein.

[0059] Detailed Description of the Invention

[0060] The term “microspheres” as used herein refers to substantially spherical discreet particles with size varying between about lOOnm to about 1mm. Also, referred to as “microcapsules” the microspheres of the present invention are characterised as having sodium nitrite as the core substance with a mixture of coating material such as ethyl cellulose (EC) and linoleic acid (LA) (as plasticiser); or zein protein and PVP (as plasticiser). The microspheres of the present invention are approximately spherical in shape but are not entirely regular with some individual particles showing adhesion of small particles to the surface of larger ones. Time of flight microscopy studies have shown almost complete coverage / coating with the encapsulating materials disclosed herein. In an embodiment the ethyl cellulose / linoleic acid coating material is added to sodium nitrite at from about 3.5 to 20% as a weight to weight ratio, such as about 3.6, 3.8, 4.0, 4.2, 4.4, 4.6,

[0061] 4.8, 5.0, 5.2, 5.4, 5.6, 5.8, 6.0, 6.2, 6.4, 6.6, 6.8, 7.0, 7.2, 7.4, 7.6, 7.8, 8.0, 8.2, 8.4, 8.6, 8.8, 9.0, 9.2, 9.4, 9.6, 9.8, 10, 10.2, 10.4, 10.6, 10.8, 11.0, 11.2, 11.4, 11.6, 11.8, 12.0, 12.2, 12.4, 12.6, 12.8, 13.0, 13.2, 13.4, 13.6, 13.8, 14.0, 14.2, 14.4, 14.6, 14.8, 15.0, 15.2, 15.4, 15.6,

[0062] 15.8, 16.0, 16.2, 16.4, 16.6, 16.8, 17.0, 17.2, 17.4, 17.6, 17.8, 18.0, 18.2, 18.4, 18.6, 18.8, 19.0 19.2, 19.4, 19.6 to about 19.8% weight to weight.

[0063] In an embodiment the amount of ethyl cellulose / linoleic acid is about 5-10% by weight relative to the amount of sodium nitrite.

[0064] In an embodiment the amount of ethyl cellulose / linoleic acid is about 5% by weight relative to the amount of sodium nitrite.

[0065] In an embodiment the zein protein / PVP coating material is added to sodium nitrite at from about 3.5 to 20% as a weight to weight ratio, such as about 3.6, 3.8, 4.0, 4.2, 4.4, 4.6, 4.8, 5.0, 5.2, 5.4, 5.6, 5.8, 6.0, 6.2, 6.4, 6.6, 6.8, 7.0, 7.2, 7.4, 7.6, 7.8, 8.0, 8.2, 8.4, 8.6, 8.8, 9.0,

[0066] 9.2, 9.4, 9.6, 9.8, 10, 10.2, 10.4, 10.6, 10.8, 11.0, 11.2, 11.4, 11.6, 11.8, 12.0, 12.2, 12.4,

[0067] 12.6, 12.8, 13.0, 13.2, 13.4, 13.6, 13.8, 14.0, 14.2, 14.4, 14.6, 14.8, 15.0, 15.2, 15.4, 15.6,

[0068] 15.8, 16.0, 16.2, 16.4, 16.6, 16.8, 17.0, 17.2, 17.4, 17.6, 17.8, 18.0, 18.2, 18.4, 18.6, 18.8,

[0069] 19.0 19.2, 19.4, 19.6 to about 19.8% weight to weight.

[0070] In an embodiment the amount of zein protein / PVP is about 5-10% by weight relative to the amount of sodium nitrite.

[0071] In an embodiment the amount of zein protein / PVP is about 5% to 10% by weight relative to the amount of sodium nitrite.

[0072] In an embodiment the microspheres of the present invention are on average between about 100 to 1000 microns. In another embodiment the microspheres are on average between about 200 to 750 microns, such as 210, 220, 230, 250, 270, 290, 310, 330, 350, 370, 380, 390, 410, 430, 450, 470, 490, 500, 510, 530, 550, 570, 590, 600, 610, 620, 630, 640, 660, 680, 690, 700, 710, 720, 730, or 740 microns, or within a range between any of the two aforementioned values. It will be appreciated that the average size of the microspheres will depend on their method of production. In an embodiment the microspheres are prepared by pan coating or fluid bed coating techniques. The term "dry mix composition" as used herein refers to the combination of a purposively selected dry palatable carrier ingredient and active toxic agent (encapsulated sodium nitrite) for the express purpose of preparing a pest control agent wherein the carrier ingredient and the toxic agent as a whole are palatable and at least partially edible by a target pig. Accordingly, the "dry mix composition" of the present invention is a purposely manufactured pest control agent which is to be contrasted with, for instance, a naturally occurring material (e.g., plant material that may contain natural quantities of sodium nitrite) and is distinguished from or, for instance, meat sausage which may contain quantities of the active agent or where the active agent is added in an unprotected form and at a very low dose for the purpose of flavour enhancement or preservation against certain bacteria such as botulinus or salmonella.

[0073] Thus the term “dry mix composition” as used herein refers to the combination of a carrier ingredient which is a pig dry feed ingredient or combination thereof, and toxic active agent for the express purpose of euthanizing a pig population wherein the carrier ingredient and the toxic active agent (in this case encapsulated sodium nitrite) when combined are palatable and at least partially edible by a farmed / domesticated pig. In relation to suitable dry palatable carrier ingredient(s) this may include grain, nuts, sugars; suitable dry plant derived components include milled grains, pollard, bran, maize (corn), plant fibres, flour, some dried fruit, vegetables, seeds, cereal and straw and mixtures thereof. As such the invention contemplates the mixing of the microencapsulated sodium nitrite into the dry palatable carrier / feed ingredient of the pig population, in quantities to provide a lethal dosage.

[0074] In an embodiment the dry mix composition is an intimately mixed combination of the microencapsulated sodium nitrite with the dry palatable carrier ingredient(s).

[0075] In an embodiment the dry mix composition is a simple combination wherein the microencapsulated sodium nitrite is added to the dry palatable carrier ingredient(s) without substantial mixing.

[0076] One of the advantages of the "dry mix composition" is realised when the density of the dry palatable carrier ingredient(s) is lower than the microencapsulated sodium nitrite. For instance, the inventors have found that ingredients such as whole or cracked wheat and whole corn has a density lower than the microencapsulated sodium nitrite. When the dry mix composition is added to a pig's feed tray, such as a well in a dispensing feed hopper, the encapsulated sodium nitrite tends to settle to the bottom of the tray or well. The inventors have found that pigs tend to ingest the lower density dry palatable carrier ingredient(s) first and then consume and lick the encapsulated sodium nitrite at bottom of the tray or well. It is often the case in other compositional arrangements, that pigs may be discouraged by the initial ingestion of sodium nitrite due to its unpleasant taste. Of course, the skilled person would appreciate that the encapsulation technique described herein circumvents this problem to a large extent. The density disparity further ensures complete voluntary consumption / ingestion of the toxic dry mix composition.

[0077] The invention relates to the humane control of feral and domestic pigs, in particular, nuisance causing feral pigs in the wild and domesticated pigs housed at a piggery. Accordingly, the terms "humane" and "humanely" as used herein refer to methods which do not cause undue distress to the target animal species. Signs of distress which are avoided or minimised by the present invention include haemorrhaging, excessive vomiting, vocalisation, severe central nervous system disruption (including hyperexcitability, convulsions, ataxia, leg trembling and leg paddling whilst prone) and prolonged death. Preferably death occurs within a few minutes up to 3 hours after ingestion of the toxic dry mix composition of the present invention with few if any symptoms other than progressive recumbency, unconsciousness, feeble breathing and death. This sequence is considered humane due to the effects of the nitrite in converting normal haemoglobin to methaemoglobin that does not transport oxygen in blood.

[0078] In relation to the present invention where the target pests are feral pig populations, the present invention contemplates the use of stable toxic dry mix compositions of the present invention to the control, cull or de-populate of feral pig populations. These a purpose made toxic dry mix composition which are able to remain stable when exposed to outside weather conditions for weeks or months at a time. In this regard the present invention also contemplates placing the toxic dry mix composition of the present invention in a target specific container or hopper which can only be accessed by a feral pig. For larger pigs, for example breeding boars at a piggery that may be 180kg or more, it may be necessary or desirable to deliver the microspheres more directly to the animal to cause death, for example by combining the microspheres with a moisture free carrier in the form of a stable suspension and administering as a drench into the mouth of the animal. In relation to the present invention where the target pests are domesticated pigs housed in a piggery the present invention contemplates the use of readily made combinations of the pig feed ingredients with the microencapsulated sodium nitrite of the present invention (i.e., toxic feed compositions) to the control of pig populations. Preferably, the combination is a dry feed combination with the microencapsulated sodium nitrite of the present invention.

[0079] It will be appreciated that the term "feral" as used herein refers target pest pig populations which live wild such that their population or numbers cannot be easily controlled. In Australia, for instance, many feral animals such as dogs, goats, cats, and pigs, were originally introduced during British settlement as either domesticated species, species suitable for hunting, or were introduced for the purpose of possibly controlling yet other pests. After escaping into the wild such animals have become feral, adopting and flourishing to life unaided by human intervention. Many feral animals are introduced species and their presence in the wild is unwanted as they can adversely affect agricultural endeavours such as crop production and grazing. Feral animals which are introduced species are distinguished from native or domesticated species. These feral animals also often cause adverse environmental impact, especially as their populations increase. Population of feral animals increase due to their vigour and survival rates, lack of natural predators and high reproduction rates and ability to adapt to a wide range of food sources. As such these feral animals have been classified as pests and it is desired to keep populations of such animals to a minimum or, where possible, to completely eradicate them from the wild or from areas of high agricultural or conservation value. It will be understood that while the toxic dry mix composition of the present invention will not be able to distinguish between feral and non- feral domesticated animals, in certain embodiments the toxic dry mix composition is only intended to be used in the control of feral pig populations and accordingly suitable measures should be taken to ensure that the toxic dry mix composition is not distributed amongst domesticated pig populations or native / protected animal species.

[0080] The term "active agent" referred to above is an agent which affects the physiology of the target feral animal in a desired manner. The active agent of the present invention is the salt sodium nitrite but it is recognised that other forms of nitrite would have similar effects and could also be used, such as for example potassium nitrite. The present invention is predicated partly on the discovery that the integrity of nitrite salt containing baits can be severely compromised due to water / moisture either (i) by insufficient coating of the nitrite granules, and / or (ii) within the toxic dry mix composition due to pH incompatibilities.

[0081] The present inventors have derived the below scheme to account for the degradation of sodium nitrite in bait products:

[0082] ® NaNO2+ HCI HNO2+ NaCl

[0083] Nitrous acid then decomposes with itself: 2HN( ' NO 2 + H2O

[0084] (thus potentially generating its own water)

[0085] ® Nitric oxide (NO) may also spontaneously and exothermically oxidise to NO2in air, then nitrogen dioxide (NO2) can react with water and yield nitric acid and more nitrous acid:

[0086] 2NO2+ H2O > 11X0. + HN02

[0087] • NaN02can also slowly oxidise to NaNOs in air and can react with amine groups to form nitrosoamines

[0088] • NaN02can also potentially depotonate water to potentially provide its own acid for reaction with itself.

[0089] In relation to the reaction scheme depicted above the acid shown (HCI) could be any acid (H+) and many bait carrier materials are characterised with acidic ingredients. Since other bait components such as wheat have a pH that is <7 it is found necessary to overcome this potential source of H+ ions. The present inventors have additionally found that stability of the bait product can be further increased by maintaining the dry mixed composition product at a pH of greater than 7. Accordingly in some embodiments the toxic dry mix compositions disclosed herein further includes a pH stability agent. The pH stability agent can be any compound which is able to maintain the pH of the dry mixed composition above pH 7 and preferably around about 7-8. Suitable stability agents include non-hygroscopic agents such as sodium carbonate (soda ash), sodium citrate, sodium acetate, sodium silicate, sodium sulphide, calcium carbonate, sodium bicarbonate, known phosphate buffers, or sodium / calcium hydroxide. In an embodiment, the pH stability agent is added at a rate of about 50-110 grams per 60kg of the entire bait composition, such as about 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84 ,85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108 or about 109 grams per 60kg of the entire toxic dry mix compositions.

[0090] In an embodiment the toxic dry mix composition has a water content of less than about 10% (w / w), such as less than 9%, less than 8%, less than 7%, less than 6%, less than 5%, less than 4%, less than 3%, or less than 2% wt / wt, or less than 1% wt / wt.

[0091] The water content of the toxic dry mix composition can be substantially minimised by predrying the components of the bait composition while formulating the finished composition.

[0092] The present inventors have found that the presence of traces of water in a nitrite based composition may lead to the build up of hydroxyl ions that can interact with some types of coatings that are sensitive to high pH, and also to the release of nitric oxide or other breakdown products arising from the reaction of nitrites with themselves or with other chemicals and / or bait components which can generate breakdown products including nitric oxide, nitrogen dioxide, nitrous acid and nitric acid that be detected by feral pigs, leading to voluntary uptake aversion. It has also been found that the salty flavour of nitrite baits compounds this problem by providing an aversive signal that limits the voluntary uptake of baits by feral pigs.

[0093] In order to improve upon known toxic baits the inventors have developed a system to avoid nitrite degradation (i.e., increase stability) and to increase the palatability to the target species. In particular, the present inventors have investigated many encapsulation ingredients and have discovered that many ingredients do not satisfactorily coat the nitrite such as to prevent / minimise leaching of the nitrite which in turn compromises the effectiveness of the end bait product. The inventors have devised specific coating techniques, such as pan coating and especially fluid bed coating, which form a more complete coating of nitrite granules specifically with ethyl cellulose and linoleic acid between ratio ranges of ethyl celluloselinoleic acid of 99: 1 to 99.99:0.01 as a % weight to weight ratio (% wt / wt) such as ethyl celluloselinoleic acid of about 99.1 :0.9, 99.2:0.8, 99.3:0.7, 99.4: 0.6, 99.5: 0.5; 99.6: 0.6; 99.7: 0.3; 99.8: 0.2; and about 99.9:0.1 and ratios in between such figures. The nitrite salt in the bait acts by causing methaemoglobin (Met Hb) formation in red blood cells, which prevents oxygen transport, and at specific doses causes rapid death by methaemoglobinaema. Accidental death by nitrite poisoning has been reported for domestic livestock such as pigs (see, for instance, Vyt, P et al, Viaams Diergeneeskundig Tijdschrift, 2005, 74, 359-363; Gibson. R., The Veterinary Record, March 22, 1975, p 270; McParland, P. J., et al, The Veterinary Record, March 1, 1980, p 201; Counters, D. E., et al, The Veterinary Record, May 3, 1975, p 412; Winks, W. R., The Queensland Journal of Agricultural Science, Vol. 7, No. 1 and 2, March and June 1950, pp 1-14; and London, W. T., et al, J.A.V.M.A, Vol 150, No. 4, pp 398-402.

[0094] From a report on the study of methemoglobin formation and reduction in various animals (see Smith & Butler., Am. J. Physiology. 210(2):347-350, 1966) it appears that the susceptibility to Met Hb formation may be related to the Met Hb reduction rate in such a way that a rapid oxidation of haemoglobin to methaemoglobin is offset by a rapid Met Hb reduction rate. In this study it was observed that pigs were particularly susceptible to methaemoglobinaema because of the pigs’ inability to effectively reduce Met Hb. The reason for this is that pigs possess relatively low levels of methaemoglobin reductase enzyme which makes them highly susceptible to methaemoglobin forming compounds.

[0095] Also, nitrite salts act as effective toxins where poisoning and death occur rapidly and relatively or perhaps even totally painlessly. The mechanism of action provides the quick development of anoxia in the brain due to the reduced oxygen carrying capacity of methaemoglobin induced by the nitrite. Thus, one of the first symptoms of the toxicosis is the occurrence of unconsciousness, in much the same way as carbon monoxide acts. Carbon monoxide leads to the formation of carboxyheamoglobin that, like methaemoglobin does not carry oxygen to tissues effectively. Carbon monoxide has been used as a method to humanely dispose of unwanted animals and is considered to be one of the most humane techniques available for this process. This is to be contrasted with the severe clinical symptoms experienced with warfarin (bleeding in various organs leads to pain, e.g. lameness, etc.), phosphorous (e.g. liver failure and serious tissue damage leading to slow lingering death which results in feeling sick for a long period of time, etc.). Also the speed of death is very quick with nitrite so any symptoms are only experienced for a short period of time. Accordingly, an advantage of the toxic dry mix compositions of the present invention are that they provide a more humane alternative to existing feral omnivore baits and that the carcasses of poisoned animals may often be clustered near to points of baiting to enable carcasses recovery or assessment of impacts. However, this advantage is only realised if a sufficient quantity of the bait is consumed and the toxic contents (i.e., nitrite) is physiologically bioavailable within a short time period. A gradual uptake of the bait will cause insufficient methaemoglobin to achieve the desired rapid lethal outcome and may reduce the activity of the animal’s activity so that further bait ingestion is disrupted. There is therefore a balance between stability of the nitrite and the ability of the encapsulated nitrite to release nitrite for effective pest control.

[0096] In an embodiment sodium nitrite used in the toxic dry mix composition of the present invention is the active agent or core material, which is presented in free-flowing granular form. It also will be appreciated that “granular” refers to a conglomeration of discrete solid, macroscopic particles. This should be contrasted with non-granular forms such as powders, liquids or flakes. Preferably the granular size of the sodium nitrite is from 200 pm to 1 mm, more preferably from 100 pm to 1mm.

[0097] Larger granules than for instance greater than 1mm, once coated, could be detected and excluded by the pig during feeding and may have lower resistance to mechanical disruption during processing such as mixing or extruding and packing. Smaller granules have a high ratio of coating to coated active ingredient and so are less suitable to the present application that requires large quantities of the active ingredient to be delivered to affect a lethal dose. The shape of the granules is typically irregular but can also be spherical. Preferably the granular form is prilled sodium nitrite. Such prilled salts are available in a commercial scale and are formed from a melted liquid. However the inventors recognised that an extruded formulation of sodium nitrite combined with a suitable binder, cut to short lengths or spheronised, would also provide a form of sodium nitrite that is suitable for coating by a fluid bed or pan coating process.

[0098] In an embodiment, prior to microencapsulation the moisture content of the sodium nitrite particles is less than 2%wt / wt, for instance, less than 1.5%wt / wt, 1.0%wt / wt, 0.9, 0.8, 0.7, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, 0.1%wt / wt or totally dry. 1 In a preferred embodiment the sodium nitrite comprises from about 5-15 wt / wt% of the toxic dry mix composition such as about 5 wt / wt%, 5.5 wt / wt%, 6 wt / wt%, 6.5 wt / wt%, 7 wt / wt%, 7.5 wt / wt%, 8.0 wt / wt%, 8.5 wt / wt%, 9.0 wt / wt%, 9.5 wt / wt%, 10 wt / wt%, 10.5 wt / wt%, 11 wt / wt%, 11.5 wt / wt%, 12 wt / wt%, 12.5 wt / wt%, 13 wt / wt%, 13.5 wt / wt%, 14 wt / wt%, 14.5 wt / wt%, or about 15 wt / wt%, or within a range between any of the two aforementioned values.

[0099] The present inventors have found that by preparing microspheres according to the present invention and delivering these microspheres into the toxic dry mix composition such that the sodium nitrite comprises from about 5-15 wt / wt%, such as about 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 wt / et% (or a range between any two of the above figures), one is able to balance the requirement to have enough sodium nitrite to provide a lethal humane dose without the risk of excessive overdosing but too much poison such that, for instance, a pig will still be attracted to the bait and find the bait palatable and will not be affected so fast as to avoid sufficient consumption of the toxic formulation.

[0100] Ethyl cellulose (EC) is a derivative of a cellulose in which some of the hydroxyl groups on the repeating glucose are presented as ethyl ether groups. The amount of ether groups may vary, for instance, between about 40-54% w / w ethoxyl.

[0101] It is however largely insoluble in water but freely stable in tetrahydrofuran, methyl acetate, chloroform, and in aromatic hydrocarbon ethanol mixture.

[0102] Without wishing to be bound by theory the present inventors surmise that the ethyl cellulose acts as a sequestering agent locking in the available water such that the nitrite is not exposed (to any great extent) to free water during the encapsulation process. 96-99% pure ethyl alcohol is economical and in the hands of the present inventors it has been shown that no appreciable increase in water content occurred in the ethyl cellulose microspheres using EC / LA / EtOH in a fluid bed process at 40°C coating air temperature, or hotter in dehumidified air stream. Either the flex stream or Wurster type fluid bed coating processes can be used but the inventors prefer the flex stream process as it allows for scaling of production. The size of the EC / LA microspheres as described herein is also seen to be a contributing factor to the stability properties for the encapsulated nitrite. If the microspheres are too big (for instance greater than 1mm) there is a potential for osmotic effects to cause swelling and self-destruction. Too small (less than lOOnm) leads to stronger coating walls which in turn may lead to insufficient release of the nitrite under physiological conditions, hampering the delivery of humane and lethal dosages and also some loss of small spheres from the coater via police filters on exit air streams.

[0103] Linoleic acid also known as LA is fatty acid with formula C18H32O2. It is often referred to by the shorthand 18:2 (n-6) or 18:2 cis-9,12.

[0104] The encapsulating material can be applied by spraying nitrite core particles with a solution of the coating material in a volatile solvent system using standard methods such as fluid bed or pan coating techniques. In certain embodiments the solvent is ethanol and in particular absolute ethanol.

[0105] Zein is a mixture of proteins derived from corn (maize) endosperm. Zein is commonly available as Amazein™ Zein is soluble in aqueous alcohols. It is however largely insoluble in water and anhydrous alcohols. It would appear impractical to attempt to coat sodium nitrite with the use of a zein / PVP mixture as this would mean the mixing of nitrite with an aqueous alcohol system as nitrite is highly hygroscopic. However, surprisingly when coating experiments were performed under these conditions no such nitrite degradation or water adsorption of the coating solution occurred. Without wishing to be bound by theory the present inventors surmise that the zein acts as a sequestering agent locking in the available water such that the nitrite is not exposed (to any great extent) to free water during the encapsulation process. Ethanol / water is economical and in the hands of the present inventors it has been shown that no appreciable increase in water content occurred in the zein microspheres using 70% ethanol / 30%water in a fluid bed process at 40°C coating air temperature, or hotter. The size of the zein / PVP microspheres as described herein is also seen to be a contributing factor to the stability properties for the encapsulated nitrite. If the microspheres are too big (for instance greater than 1mm) there is a potential for osmotic effects to cause swelling and self-destruction. Too small (less than lOOnm) leads to stronger coating walls which in turn may lead to insufficient release of the nitrite under physiological conditions, hampering the delivery of humane and lethal dosages.

[0106] PVP also known as polyvidone or povidone is a water-soluble polymer made from monomer N-vinylpyrrolidone, and is a known plasticizer in formulation chemistry.

[0107] The encapsulating material can be applied by spraying nitrite core particles with a solution of the coating material in a volatile solvent system using standard methods such as fluid bed or pan coating techniques. In an embodiment encapsulated nitrite comprises about 2-15% wt / wt of the toxic dry mix composition, for instance about 2.5% wt / wt, 3.5% wt / wt, about 4% wt / wt, about 4.5% wt / wt, about 5% wt / wt, about 5.5% wt / wt, about 6% wt / wt, about 6.5% wt / wt, about 7% wt / wt, about 7.5% wt / wt, about 8% wt / wt, about 8.5% wt / wt, about 9% wt / wt, about 9.5% wt / wt, about 10% wt / wt, about 11% wt / wt, about 12% wt / wt, about 13% wt / wt, about 14% wt / wt, or about 15% wt / wt, or within a range between any of the two aforementioned values.

[0108] In an embodiment the encapsulated nitrite composition comprises about 2-10% wt / wt of the final toxic dry mix composition (i.e., dry palatable carrier ingredient(s) and microencapsulated sodium nitrite).

[0109] In an embodiment the encapsulated nitrite composition comprises about 2-20% wt / wt of the final toxic dry mix composition (i.e., dry palatable carrier ingredient(s) and microencapsulated sodium nitrite).

[0110] The encapsulated nitrite granules according to the present invention relating to toxic dry mix composition can be mixed with an additional lipophilic carrier. The lipophilic carrier can be selected from the group consisting of lipophilic surfactants, vegetable oils, fatty acids and esters, fatty alcohol, glycerides, waxes and the like.

[0111] It would be appreciated however that the optional additional lipophilic carrier would need to be at least also palatable to pigs and preferably palatable and attractive. In this regard the preferred lipophilic carrier is selected from vegetable oils and lipid based materials. In an embodiment selected from the group consisting of castor oil, peanut oil, corn oil, linseed oil, and sesame oil.

[0112] In an embodiment the lipophilic carrier is a peanut oil paste (or just “peanut paste”) and hence the toxic dry mix composition may be in the form of a paste. Peanut paste is known in the food arts as a base material for peanut butter and is formed by roasting, blanching, and grinding raw peanuts so the paste contains peanut endosperm and peanut oil. In combination, with the encapsulated microspheres of the present invention, the present inventors have found that the stability of the nitrite with the toxic dry mix composition, and therefore the toxic dry mix composition itself, is greatly improved. In an embodiment encapsulated nitrite comprises about 2-15% wt / wt of the finished toxic dry mix composition, for instance about 2.5% wt / wt, 3.5% wt / wt, about 4% wt / wt, about 4.5% wt / wt, about 5% wt / wt, about 5.5% wt / wt, about 6% wt / wt, about 6.5% wt / wt, about 7% wt / wt, about 7.5% wt / wt, about 8% wt / wt, about 8.5% wt / wt, about 9% wt / wt, about 9.5% wt / wt, about 10% wt / wt, about 11% wt / wt, about 12% wt / wt, about 13% wt / wt, about 14% wt / wt, or about 15% wt / wt, or within a range between any of the two aforementioned values.

[0113] It is desirable to have a finished toxic dry mix composition product that provides for usable shelf storage life at room temperatures or field temperatures but that is not so completely coated and shielded that the coating acts to disrupt the quick release of the active ingredient into the pig stomach soon after ingestion. This is because sodium nitrite is a mass active agent that will only induce lethal levels of methaemoglobinaemia if it is dumped quickly into the target animal system. A gradual delivery of a theoretically lethal acute dose will not reliably achieve the level of methaemoglobinaeimia needed for death. Thus, in devising a protective coating a balance must be struck between protecting the nitrite from degradation or interaction with bait components and at the same time allowing for rapid bioavailability of the toxin once the bait is taken.

[0114] In an embodiment the toxic dry mix composition is a dry free-flowing solid.

[0115] In another embodiment the toxic dry mix composition is a loose free-flowing solid dry combination of dry palatable carrier ingredient and the encapsulated sodium nitrite.

[0116] It will be appreciated that during typical baiting campaigns multiple baits are dispersed within the area of foraging of the target animal species. A single bait may not provide a lethal dose to a single target animal even if completely consumed. Preferably however the nitrite salt is in an amount which provides a lethal dose to a target feral animal after consumption of a small quantity of the toxic dry mix composition. That is, the quantity of nitrite salt in a single portion of toxic dry mix composition or a single edible portion of a larger amount of a toxic dry mix composition offering is such that it will effectively kill a feral omnivorous animal. In an ideal situation a single pig in the population does not eat too much of the toxic dry mix composition or monopolise the toxic dry mix composition to the exclusion of others in the population, but only eats an amount that is required to kill the pig. This enables many pigs in the population to be killed from a single offering of the toxic dry mix composition and also minimises excessive poison loads within a single carcass. It will be appreciated that humanely euthanizing a farmed / domesticated pig population the toxic dry mix composition is administered in the normal way the pigs would expect to be feed. Preferably, a feeding provides a lethal dose. Preferably however the nitrite salt is in an amount which provides a lethal dose to a target pig animal after consumption of a small quantity of the toxic dry mix composition. That is, the quantity of nitrite salt in a single feeding or a single edible portion is such that it will effectively kill one or more pigs in the pig population.

[0117] In certain embodiments the pig population ingests an average dose of the toxic dry mix composition at a rate of 20-60g / pig (based on a 50kg pig size) or approximately 500- 900mg / kg representing a certain overdose for quick effect. For such pigs it is possible to achieve 100% deaths within a mean of 2 hours of ingestion.

[0118] It will be appreciated that this time frame between feeding farmed / domesticated pigs, for example within a piggery, allows sufficient time for the pigs to be moved to an area (while they are still able to walk), where collection and removal of the carcasses can be facilitated after death. This provides significant advantages over current methods of culling which involve collection of the carcasses from their pens and removal of associated blood, these being steps that can also contribute to the spread of disease within the piggery.

[0119] The selection of toxic dry mix composition components must also consider the moisture content of the carrier material or attractive agent.

[0120] The toxic dry mix composition may also include specific chemical attractants, such as flavourants or scented substances (odourants). The toxic dry mix composition may also comprise other additives known in the art such as colourants, preservatives, binders, fillers, and the like. The choice of colorants is important as nitrite can react with agents that contain amide groups and once exposed to water nitrite can produce an alkaline solution that can change the colours of some dyes. The use of an inert and stable dye is preferred. For instance, in a preferred embodiment the carrier material contains a colourant (dye) which makes the bait black in colour to mask the bait from non-target species such as birds which generally have a preference for eating yellow and red coloured food consistent with ripe fruit. For instance, in an embodiment the toxic dry mix composition comprises an amount of an inert colorant to turn the composition to grey or black. The selection of a colourant must also have regard to cost and the potential for reaction between the active ingredient sodium nitrite and the colourant. Ferric oxide is an inert colorant that is suitable for this purpose, whereas dyes containing amide groups are less suitable because of their potential to react with the active ingredient. Water soluble dyes cannot be used easily. Also, preservatives, antioxidants, and binding agents may be added to provide mechanical strength to the finished toxic dry mix composition and to reduce the risk of premature degradation on storage.

[0121] The inventors also found effective that the method can be carried out when the dry palatable carrier ingredient is bound to the microencapsulated sodium nitrite microspheres with a low moisture lipophilic binding agent which is also palatable to the target pig population.

[0122] Such binding agents may be molasses, sesame oil, canola oil or the like.

[0123] Accordingly, in an aspect the invention provides a method of humanely de-populating a population of pigs including the step of providing to said population of pigs a toxic composition comprising microencapsulated sodium nitrite microspheres that are bound to one or more dry palatable carrier ingredient with a low moisture lipophilic binding agent, wherein the microencapsulated sodium nitrite microspheres are encapsulated by a coating material comprising ethyl cellulose / linoleic acid (EC / LA) microencapsulated sodium nitrite microspheres, wherein the ratio range of ethyl cellulose to linoleic acid is in an amount from about 99: 1 to about 99.99: 0.01 as a % weight to weight ratio.

[0124] Accordingly, in an aspect the invention provides a method of humanely de-populating a population of pigs including the step of providing to said population of pigs a toxic composition comprising microencapsulated sodium nitrite microspheres that are bound to one or more dry palatable carrier ingredient with a low moisture lipophilic binding agent, wherein the microencapsulated sodium nitrite microspheres are encapsulated by a coating material comprising zein protein and PVP in an amount from about 95:5 to about 99.5:0.5 as a % weight to weight ratio.

[0125] In certain embodiments the pig population ingests an average dose of the toxic composition at a rate of 20-60g / pig (based on a 50kg pig size) or approximately 500-900mg / kg representing a certain overdose for quick effect. For such pigs it is possible to achieve 100% deaths within a mean of 2 hours of ingestion.

[0126] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates. Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0127] Certain embodiments of the invention will now be described with reference to the following examples which are intended for the purpose of illustration only and are not intended to limit the scope of the generality hereinbefore described.

[0128] Examples

[0129] Example 1: Preparation of an Encapsulated NaNCh with ethyl cellulose / linoleic acid

[0130] Methods

[0131] Encapsulating granules

[0132] NaNCh (SN) granules (food grade E250, BASF) approximately 0.2-1.0 mm and EC were used as supplied. The BASF SN is free flowing and has an anticaking agent (amorphous silicone dioxide at about 0.1% w / w). The SN was pre-sieved to achieve a more uniform particle size range from 100 to 1000 microns diameter by removing the fines (<100 microns). NaNCh granules (500 g) were coated using a pan coating process with EC (9.975%, or 9.95%, or 9.90%) dissolved in 95-96% ethanol (90%) and LA was added at 0.025%, or 0.05%, or 0.10% to make a mixture containing EC and LA. To coat the NaNCh, 500 g of granules were placed in a spherical pan, the pan was rotated at 20 revolutions per minute, the liquid encapsulant solution was sprayed onto the granules at one litre per hour while the whole was warmed to 40°C by warm pre-dried air directed onto the granule bed to progressively evaporate the solvents. Once all coating material was applied the granules continued to be rotated to ensure drying.

[0133] Example 2: Preparation of an encapsulated Na NO 2 with ethyl cellulose / linoleic acid

[0134] Prilled sodium nitrite with a moisture content of less than 1% (typically around 0.2 to 0.3%) and a particle size distribution of 180 to 800 microns is suspended as a fluidised bed in a stream of air drawn into the coating apparatus at 80% relative humidity at 12°C and which is pre-heated heated to 40 to 45°C. Coating material for EC is prepared by fully dissolving 9.95% w / w EC in 96% ethyl alcohol and containing 0.05% LA as a plasticiser to form the coating solution.

[0135] The coating solution is sprayed on the fluidised bed of sodium nitrite granules initially at a low rate initially and then at a progressively increasing rate to provide an even and uniform coating layer until 2.5 to 25% coating of the particles with EC / LA is achieved, typically 5% or 10%w / w of the finished product. A finished coated microsphere product prepared according to this example containing 95% sodium nitrite and 5% EC / LA is further dried by a flow of heated air to remove all solvents prior to packing. A further finished coated microsphere product that is 90% sodium nitrite and 10% EC / LA is also further dried by a flow of heated air to remove all solvents prior to packing. A thicker coating can provide better protection against moisture ingress. Storage of the microspheres at temperatures below about 8°C, for example about 4 °C, can also extend the shelflife of the microspheres, as well as formulated products prepared from the microspheres. Variations on the above method that produced EC / LA microencapsulated sodium nitrite microspheres with various % coating of zein are also readily achieved.

[0136] Example 3: Dry mix compositions comprising microencapsulated sodium nitrite and dry palatable carrier

[0137] The coated nitrite is then formulated with a dry palatable carrier that further protects the nitrite from degradation and offers the mixture in a palatable form for feral or domestic pig to eat. In this carrier bait consists of an intimate admixture of dried ground cereals including wheat, com, or wheat flour and peanut paste including some peanut oil to produce a dry mix paste composition. The final concentration of nitrite in the finished composition was about 10% wt / wt so that a pig is killed if it eats in the region of 15 to 200 grams of the dry mix composition. The dry mix composition may be packaged into trays that allow ready access to the pigs, or prepared on site, e.g. at the piggery.

[0138] Alternatively, a palatable bait containing sodium nitrite is prepared by mixing cracked wheat, fine crushed maize, white wheat flour, sugar, inert colourant and sodium carbonate (as a pH modifier) until uniform colour is achieved in a ribbon blender. Then the required quantity of microencapsulated sodium nitrite microspheres is added and fully mixed with the dry ingredients. Example 4: On-farm experiment of administering microencapsulated sodium nitrite to grower pigs

[0139] Methods

[0140] Twenty-four grower pigs of similar age and weight (approximately 50 kg) were randomly assigned to two treatment groups (n = 12 per group). Each group was subdivided into three replicate pens, with four pigs per pen. Pens were visually shielded from one another to prevent pigs in untreated pens from observing treatment-related events.

[0141] A pre-feeding period was implemented to habituate pigs to accept food presented in a novel form, frequency, and / or volume. The lethal phase commenced once pigs consistently consumed at least 90% of their feed within 30 minutes of presentation but more than 80% consumption of the novel feed was achieved within one day.

[0142] Paste treatment: A paste formulation of microencapsulated sodium nitrite was presented to pigs (hereafter, pigs in the paste treatment are referred to as "paste pigs"). The paste comprised commercially available HOGGONE® paste (10% w / w microencapsulated sodium nitrite in a peanut-flavoured paste, manufactured by Animal Control Technologies Australia Pty Ltd). An average dose of 900 mg / kg bodyweight, corresponding to 450 g / pig of HOGGONE® paste, was offered.

[0143] Granular treatment: In a separate set of 3 pens containing 4 weaner pigs per pen, a granular formulation of microencapsulated sodium nitrite was presented to pigs as a top dressing over conventional pig feed pellets (hereafter, pigs in the granular treatment are referred to as "granule pigs"). The granules consisted of 100% microencapsulated sodium nitrite, identical to the active ingredient used in HOGGONE® paste, the granules or microspheres themselves comprising 90% sodium nitrite and 10% EC / LA . The microencapsulated sodium nitrite used in the present invention was prepared as described in Patent WO 2022 / 087684. An average dose of 800 mg / kg body weight, corresponding to 40 g / pig of granules, was applied as a top dressing over a 400 g feed portion.

[0144] Results

[0145] Each pig was continuously observed by an assigned veterinarian investigator. Standardized qualitative behavioural assessments were conducted at 15-minute intervals for each pig.

[0146] Paste pigs consumed approximately 80% of HOGGONE® paste within 30 minutes, with an average intake of 380 g per pig (-722 mg / kg bodyweight). Median times to first down, last down, non-responsiveness and death were approximately 26, 58, 67 and 74 minutes, respectively. The mean time to death was 78 minutes.

[0147] Granule pigs consumed approximately 100% of their feed within 10 minutes, with an average intake of 40 g of granules per pig (-769 mg / kg bodyweight). Median times to first down, last down, non-responsiveness and death were approximately 35, 73, 89 and 97 minutes, respectively. The mean time to death was 100 minutes.

[0148] Both treatment groups achieved 100% mortality without veterinary intervention. Survival analysis indicated that paste pigs experienced each key event earlier than granule pigs. Unrestricted access to water did not impact outcomes, and no abnormal drinking behaviours were observed.

[0149] Post-mortem examination revealed characteristic signs of severe anoxia in all deceased pigs. Reddening of the stomach lining was typically observed in 1-2 pigs per pen, though no other gross clinical abnormalities were observed. Histopathology of heart, spleen, kidney, skeletal muscle, lung, and liver samples revealed no changes of clinical significance. Tissue samples submitted for nitrite / nitrate residue testing indicated that the highest concentrations were detected in stomach linings and contents, while residue levels in all other tissues posed negligible risk of secondary nitrite / nitrate poisoning to carcass scavengers.

[0150] Both treatments achieved humane, efficient depopulation of grower pigs without the need for individual animal handling. Compared to the paste treatment, the granular treatment provided a slightly longer time window (approximately 30 minutes) to safely move pigs to a suitable location, facilitating easier carcass removal and disposal.

[0151] The results are described in further detail in Tables 1 to 3 below:

[0152] Table 1. Description of pre-feeding regime used to reduce feeding frequency to once daily, to reduce feed volume to maintenance only, and to transition paste-pigs from dry feed to paste.

[0153] Table 2. meSN dosage and consumption for each treatment group.

[0154] Table 3. The minimum, maximum, and median time for each event for each treatment group. The hazard ratios and 95% CI from the Cox proportional hazard test are also shown.

[0155] Example 5: Field trial of administering microencapsulated sodium nitrite to trapped feral pigs

[0156] Testing lots from mixed bags of corn (100 g) with about 40 g of encapsulated sodium nitrite

[0157] Tested in hoppers on trapped feral pigs

[0158] The tested pigs were fed corn for two days before given toxic feed

[0159] Pens Qty of Pigs in each Pen Toxic Feed (Night 1) Toxic Feed (Night 2)

[0160] Pen 1 3 1 of 3 died (one pig injured and euthanized, the remaining pig transferred to pen 2)

[0161] Pen 2 4 1 of 4 died 3 of 4 died

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A method of humanely de-populating a population of pigs including the step of providing to said population of pigs a dry mix composition comprising microencapsulated sodium nitrite microspheres and one or more dry palatable carrier ingredient, wherein the microencapsulated sodium nitrite microspheres are encapsulated by a coating material comprising ethyl cellulose / linoleic acid (EC / LA) microencapsulated sodium nitrite microspheres, wherein the ratio range of ethyl cellulose to linoleic acid is in an amount from about 99: 1 to about 99.99: 0.01 as a % weight to weight ratio.

2. A method of humanely de-populating a population of pigs including the step of providing to said population of pigs a dry mix composition comprising microencapsulated sodium nitrite microspheres and one or more dry palatable carrier ingredient, wherein the microencapsulated sodium nitrite microspheres are encapsulated by a coating material comprising zein protein and PVP in an amount from about 95:5 to about 99.5:0.5 as a % weight to weight ratio.

3. A method of humanely de-populating a population of pigs including the step of providing to said population of pigs a dry mix composition comprising microencapsulated sodium nitrite microspheres and one or more dry palatable carrier ingredient, wherein the microencapsulated sodium nitrite microspheres are encapsulated by a coating material comprising ethyl cellulose / linoleic acid (EC / LA) microencapsulated sodium nitrite microspheres, wherein the ratio range of ethyl cellulose to linoleic acid is in an amount from about 99: 1 to about 99.99: 0.01 as a % weight to weight ratio and the ethyl cellulose / linoleic acid coating material is added to the nitrite salt to form the microspheres at from about 2.5 to 30% weight to weight based on ethyl cellulose / linoleic acid to nitrite salt.

4. A method of humanely de-populating a population of pigs including the step of providing to said population of pigs a dry mix composition comprising microencapsulated sodium nitrite microspheres and one or more dry palatable carrier ingredient, wherein the microencapsulated sodium nitrite microspheres are encapsulated by a coating material comprising zein protein and PVP in an amount from about 95:5 to about 99.5:0.5 as a % weight to weight ratio, wherein the zein protein / PVP coating material is added to the nitrite salt to form the microspheres at from about 3.5 to 20% weight to weight based on zein protein / PVP to nitrite salt.

5. A method of anyone of claims 1 to 4 wherein the dose of the dry mix composition is at a rate of about 20-60g sodium nitrite / pig (based on a 50kg pig size) or about 500- 900mg of sodium nitrite / kg.

6. A method of anyone of claims 1 to 5 wherein the sodium nitrite comprises from about 5-15 wt / wt% of the toxic dry mix composition7. A method of humanely de-populating a population of pigs including the step of providing to said population of pigs a dry mix composition comprising microencapsulated sodium nitrite microspheres and one or more dry palatable carrier ingredient, wherein the microencapsulated sodium nitrite microspheres are encapsulated by a coating material comprising ethyl cellulose / linoleic acid (EC / LA) microencapsulated sodium nitrite microspheres, wherein the ratio range of ethyl cellulose to linoleic acid is in an amount from about 99: 1 to about 99.99: 0.01 as a % weight to weight ratio and the ethyl cellulose / linoleic acid coating material is added to the nitrite salt to form the microspheres at from about 2.5 to 30% weight to weight based on ethyl cellulose / linoleic acid to nitrite salt, wherein the dry mix composition is provided at a rate of 20g-60g sodium nitrite / pig (based on a 50kg pig size) or approximately 500-900mg sodium nitrite / kg, and wherein the sodium nitrite comprises from about 5-15 wt / wt% of the dry mix composition.

8. A method of humanely de-populating a population of pigs including the step of providing to said population of pigs a dry mix composition comprising microencapsulated sodium nitrite microspheres and one or more dry palatable carrier ingredient, wherein the microencapsulated sodium nitrite microspheres are encapsulated by a coating material comprising zein protein and PVP in an amount from about 95:5 to about 99.5:0.5 as a % weight to weight ratio, wherein the zein protein / PVP coating material is added to the nitrite salt to form the microspheres at from about 3.5 to 20% weight to weight based on zein protein / PVP to nitrite salt, wherein the dry mix composition is provided at a rate of 20g-60g of sodium nitrite / pig (based on a 50kg pig size) or approximately 500-900mg of sodium nitrite / kg, and wherein the sodium nitrite comprises from about 5-15 wt / wt% of the dry mix composition.

9. A method according to any one of claims 1 to 8, wherein the dry composition mixture is characterised with a pH of greater than pH 7.

10. A method of humanely de-populating a population of pigs including the step of providing to said population of pigs a dry mix composition comprising microencapsulated sodium nitrite microspheres and one or more dry palatable carrier ingredient, wherein the microencapsulated sodium nitrite microspheres are encapsulated by a coating material comprising ethyl cellulose / linoleic acid (EC / LA) microencapsulated sodium nitrite microspheres, wherein the ratio range of ethyl cellulose to linoleic acid is in an amount from about 99: 1 to about 99.99: 0.01 as a % weight to weight ratio and the ethyl cellulose / linoleic acid coating material is added to the nitrite salt to form the microspheres at from about 2.5 to 30% weight to weight based on ethyl cellulose / linoleic acid to nitrite salt, and wherein the dry mix composition is characterised with a pH>7.

11. A method of humanely de-populating a population of pigs including the step of providing to said population of pigs a dry mix composition comprising microencapsulated sodium nitrite microspheres and one or more dry palatable carrier ingredient, wherein the microencapsulated sodium nitrite microspheres are encapsulated by a coating material comprising zein protein and PVP in an amount from about 95:5 to about 99.5:0.5 as a % weight to weight ratio, wherein the zein protein / PVP coating material is added to the nitrite salt to form the microspheres at from about 3.5 to 20% weight to weight based on zein protein / PVP to nitrite salt, and wherein the dry mix composition is characterised with a pH>7.

12. A method according to anyone of claims 1 to 11 wherein the dry palatable carrier ingredient(s) used in the dry mix composition is / are characterised as having a lower density compared to the microencapsulated sodium nitrite.

13. A method according to anyone of claims 1 to 12 wherein the dry palatable carrier ingredient(s) are selected from whole grains, such as wheat and corn.

14. A method according to anyone of claims 1 to 13 wherein the pig population is a domestic pig population which has been exposed to or is suspected to have been exposed to a contagious disease, selected from Foot and Mouth Disease (FMD), African Swine Fever (ASF), classic swine fever (CSF), Influenza A virus, Pseudorabies, Japanese Encephalitis Virus (JEV) or Swine Brucellosis.

15. A method of humanely de-populating a population of pigs including the step of providing to said population of pigs a toxic composition comprising microencapsulated sodium nitrite microspheres that are bound to one or more dry palatable carrier ingredient with a low moisture lipophilic binding agent, wherein the microencapsulated sodium nitrite microspheres are encapsulated by a coating material comprising ethyl cellulose / linoleic acid (EC / LA) microencapsulated sodium nitrite microspheres, wherein the ratio range of ethyl cellulose to linoleic acid is in an amount from about 99: 1 to about 99.99: 0.01 as a % weight to weight ratio.

16. A method of humanely de-populating a population of pigs including the step of providing to said population of pigs a toxic composition comprising microencapsulated sodium nitrite microspheres that are bound to one or more dry palatable carrier ingredient with a low moisture lipophilic binding agent, wherein the microencapsulated sodium nitrite microspheres are encapsulated by a coating material comprising zein protein and PVP in an amount from about 95:5 to about 99.5:0.5 as a % weight to weight ratio.

17. A method according to claim 15 or 16 the pig population ingests a dose of the toxic composition at about 20-60g / pig (based on a 50kg pig size) or approximately 500- 900mg / kg.

18. A method according to anyone of claims 15 to 17 wherein the binding agent is selected from molasses, sesame oil, canola oil or the like.

Images