A new study published in Chemosphere has shown that carprofen (from the same family of drugs as diclofenac and meloxicam) is also toxic to vultures. Frequent and widespread use of diclofenac to treat cattle and buffalo in South Asia was found to be responsible for catastrophic population declines in vultures that consumed livestock carcasses. Conversely, a similar drug, meloxicam was shown in clinical trials not to kill vultures at the maximum level of exposure in a carcass. However, tens of drugs belong 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 drugs are vulture-toxic and which are vulture-safe to inform advocacy activities globally. With this impetus, scientists from South Africa and the United Kingdom, including scientists from the RSPB Centre for Conservation Science, undertook a clinical trial of carprofen.
Professor Vinny Naidoo, a co-author of the study and Director of the Biomedical Research Centre, University of Pretoria, South Africa, says: “We wanted to safety test carprofen because we had some evidence that this drug might be non-toxic to vultures. This could have provided vets and farmers another vulture-safe alternative to diclofenac.”
In a controlled experiment, vultures were given kidney tissue rich in carprofen or 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. However, the researchers found that carprofen concentrations were much higher at the injection site than in the kidneys or liver of the cattle used in the experiment. Further, concentrations at the injection sites varied among cattle. One of two vultures exposed to the average concentration found at the injection site died. Post mortem examination found severe kidney and liver damage evident of NSAID poisoning.
“NSAID safety testing provides the critical evidence needed to bring about bans and save tens of thousands of vultures,” says Toby Galligan, a co-author of the study and Senior Conservation Scientist at the RSPB Centre for Conservation Science, UK. “We carefully design the testing to minimise the number of vultures that may die.”
The researchers concluded that carcasses of cattle treated with carprofen were generally harmless to vultures; however, cattle vary in their absorption of the drug, resulting in some having very high concentrations at the injection site; and vultures vary in their elimination of the drug, resulting in some suffering renal failure and death. In summary, some vultures will die from eating some carcasses of cattle treated with carprofen. While carprofen is not as toxic to vultures as diclofenac, it is also not as vulture-safe as meloxicam.
“We are talking about endangered and critically endangered species of vulture – we cannot afford to lose any to carprofen,” says Kerri Wolter, a co-author of the study and founder of South African vulture conservation organisation VulPro. “Therefore, carprofen should not be used to treat livestock in regions where the carcasses of these livestock are provided to vultures.”
Yet, carprofen is commonly used to treat livestock in South Africa where vultures are endangered and critically endangered and livestock carcasses are provided to them at numerous feeding stations. In South Asia, carprofen is usually only recommended for use in dogs, but 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.
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