http://www.extension.org/67572 With disease issues, the decline of the rendering industry, a ban on use of downer cows for food, and rules to halt horse slaughter, environmentally safe and sound practices for disposal of horses and other livestock mortalities are limited. Improper disposal of carcasses containing veterinary drugs has resulted in the death of domestic animals and wildlife. Composting of carcasses has been performed successfully to reduce pathogens, nutrient release, and biosecurity risks. However, there is concern that drugs used in the livestock industry, as feed additives and veterinary therapies do not degrade readily and will persist in compost or leachate, threatening environmental exposure to wildlife, domestic animals and humans.
Two classes of drugs commonly used in the livestock and horse industries include barbiturates for euthanasia and non-steroidal anti-inflammatory drugs (NSAID) for relief of pain and inflammation. Sodium pentobarbital (a barbiturate) and phenylbutazone (an NSAID) concentrations in liver, compost, effluent and leachate were analyzed in two separate horse carcass compost piles in two separate years. Horse liver samples were also buried in 3 feet of loose soil in the first year and drug concentrations were assessed over time.