Collapse of Asian vulture populations: risk of mortality from residues of the veterinary drug diclofenac in carcasses of treated cattle.

1. The populations of three species of South Asian vultures (Gyps bengalensis, Gyps indicus and Gyps tenuirostris) have declined rapidly within the last decade and all are now critically endangered. Veterinary use of the non-steroidal anti-inflammatory drug diclofenac appears to be a major cause of the declines. Vultures are likely to be exposed to the drug when they feed on carcasses of livestock that were treated with diclofenac before death.

2. We measured the concentration of diclofenac in the tissues of treated Indian humped and European cattle (Bos indicus and Bos taurus) in relation to the interval between dosing and death. We used a dose-response model to assess the risk posed to wild vultures if they feed on carcasses of treated livestock.

3. Diclofenac concentrations in fat, intestine, kidney and liver were considerably higher than those in muscle, but concentrations in the first four tissues initially depleted more rapidly (half-life 6-8 h) with time since the last injection of the drug, compared with muscle (half-life 15 h). Depletion rates became much slower in all tissues 25-98 h after the last injection.

4. Diclofenac concentration, averaged across the carcass, was enough to cause appreciable mortality (> 10% of birds per meal) if oriental white-backed vultures G. bengalensis were to take a large meal from the carcass of an animal that was given its last dose of the drug within a day or two before death. Vultures that feed selectively on tissues with high concentrations of the drug, such as kidney, liver and intestine, would be exposed to a higher risk and for longer after dosing.

5. Synthesis and applications. The tissues of cattle treated with diclofenac are a hazard to wild vultures that feed on an animal that dies within a few days after treatment. Intestine, kidney and liver have the highest diclofenac concentrations, but the concentration averaged across all the edible tissues of the carcass is also hazardous. Withdrawal of diclofenac from veterinary use on animals whose carcasses may become available to scavenging vultures is recommended. In ex situ and in situ conservation projects, vultures should be fed on carcasses of animals that are known not to have been treated with diclofenac in the week before death.