A new study finds another veterinary painkiller is toxic to vultures

Blog by Dr Toby Galligan, Senior Conservation Scientist, RSPB Centre for Conservation Science

Frequent and widespread use of diclofenac to treat cattle and buffalo in South Asia during the 1990’s and 2000’s was responsible for catastrophic population declines in vulture that consumed livestock carcasses. Five species of South Asian vulture are now endangered or critically endangered.

Another drug from the same family, meloxicam, was shown in clinical trials not to kill vultures at the maximum level of exposure in a carcass. However, there are tens of drugs belonging to this family, known as non-steroidal anti-inflammatory drugs or NSAIDs, and the toxicity of most remains unknown.

Conservationists are desperate to know which are vulture-toxic and which are vulture-safe to inform advocacy activities globally. With this impetus, we worked with scientists from South Africa and other institutes in the UK, to undertake a clinical trial of the NSAID carprofen, and our paper has just been published online in the scientific journal Chemosphere.

NSAID safety testing provides the critical evidence needed to bring about bans and save tens of thousands of vultures. We carefully designed our testing to minimise the number of vultures that would die. We gave vultures kidney tissue rich in carprofen and pure carprofen at the maximum levels measured in kidney tissue. These vultures showed no toxicity. NSAID concentrations are typically highest in the kidney or liver of livestock carcasses, so that was an initial good sign. However, we found that carprofen concentrations were much higher at the injection site rather than in the kidneys or liver of the cattle used in the experiment. Further, concentrations at the injection sites varied among cattle. Sadly, one of two vultures exposed to the average concentration found at the injection site died. Post mortem examination of this vulture found severe kidney and liver damage, which is evidence for NSAID poisoning.

We concluded that carcasses of cattle treated with carprofen were generally harmless to vultures. However, cattle vary in their absorption of the drug and have a very high concentrations at the injection site; and vultures vary in their elimination of the drug, resulting in some suffering renal failure and death. Some vultures will die from eating some carcasses of cattle treated with carprofen, particularly if they feed on the tissues from the injection site. While carprofen is not as toxic to vultures as diclofenac, it is also not as vulture-safe as meloxicam.

Photo: Cape vultures (Gyps coprotheres) and other scavenging birds feeding at VulPro’s feeding station. Here the carcasses are carprofen-free, but elsewhere in South Africa and South Asia the carcasses may contain vulture-killing doses of carprofen.   

Another of my co-authors, Kerri Wolter, who is the founder of South African vulture conservation organisation VulPro said “we are talking about endangered and critically endangered species of vulture – we cannot afford to lose any to carprofen”. Therefore, injectable carprofen should not be used to treat livestock in regions where the carcasses of these livestock are provided to vultures.

Yet, carprofen is still commonly used to treat livestock in South Africa where vultures are endangered and critically endangered and livestock carcasses are often provided to them at numerous feeding stations. In South Asia, carprofen is recommended for use in dogs only, but there, unqualified para-vets often ignore recommendations as evident by their misuse of diclofenac intended for humans.

The peer-reviewed paper on this study can be accessed online through ScienceDirect at https://doi.org/10.1016/j.chemosphere.2017.08.167