Last week, I wrote about the veterinary NSAID diclofenac, present in livestock carcasses, as a cause of precipitous declines in Gyps vulture populations in South Asia. Across the Indian subcontinent, populations of White-backed, Long-billed, and Slender-billed Vultures have diminished by over 95% since the early 1990s, and all are now considered to be critically endangered. Based on skull, beak, and mandibular morphologies, these griffon vultures fall into the behavioral category of “gulpers”, and feed primarily on the viscera and muscles of ungulate carcasses (Hertel, 1994).
In South Asia, domestic animals were routinely treated with diclofenac to relieve fever, inflammation, and pain, and Gyps vultures that consumed carcasses of these animals developed kidney failure and visceral gout from the diclofenac exposure. Because of the devastating effects of this veterinary drug on vulture populations in India, licenses to manufacture and market diclofenac were withdrawn in 2006. To assess residual levels of diclofenac that might affect the critically endangered remaining vultures, Taggart and colleagues (2007) measured the NSAID in liver samples from livestock carcasses across several states in India. Approximately 10% of carcasses sampled, in particular those of Indian cows and water buffalos, contained significant concentrations of diclofenac. The investigators estimated that 50 to 100 million animals per year would be expected to die and to be available to vultures in India, with 0.02% containing detectable and potentially toxic levels of dicofenac. Unfortunately, several alternative NSAIDs, such as carprofen and flunixin, may be toxic for other vulture species, including the Egyptian Vulture (Neophron percnopterus) and the Red-headed Vulture (Sarcogyps calvus) in South Asia (Taggart et al., 2007).
African White-backed Vultures (Gyps africanus), used by Swan et al. (2006) to assess the toxicity of meloxicam in griffon vulture species
Photo: Institute of Biology
Are there veterinary NSAIDs that can be used to treat pain and inflammation effectively in livestock, and that are not toxic to vultures that might feed on carcasses? Swan and colleagues (2006) used captive African White-backed Vultures (Gyps africanus), which are as susceptible to diclofenac poisoning as are their Indian congeners (G. bengalensis, G. indicus), to identify a possible alternative, meloxicam. In the first phases of the study, meloxicam was administered to captive G. africanus vultures by gavage (oral administration to the crop, via a tube), and the health of these birds was closely monitored. All fifteen meloxicam-treated birds survived, with no elevation in serum concentrations of uric acid (indicative of kidney failure and impending visceral gout), and thus the study moved on to phases IV and V. Phase IV involved larger numbers of both captive and wild-caught African White-backed Vultures, which received meloxicam by gavage, and none of the birds displayed any adverse responses to this drug. In the final phase (V) of the study, vultures were given liver from cattle that had been injected with meloxicam for several days prior to slaughter, and again, the G. africanus birds survived, and had no evidence of elevated serum uric acid levels. A few of the endangered Asian Gyps vultures also received meloxicam by gavage, and suffered no apparent ill effects. The researchers concluded that the NSAID meloxicam is much less toxic than diclofenac for three Gyps vulture species, and is in fact likely to be safe for other vultures, raptors, and scavenging bird species. Swan and colleagues recommended that governments advocate use of meloxicam, to replace diclofenac, and that establishment of captive breeding populations of South Asian Gyps vultures is an important step for saving these species.
Hertel, F. (1994). Diversity in body size and feeding morphology within past and present vulture assemblages. Ecology 75(4), 1074-1084.
Taggart, M.A., Senacha, K.R., Green, R.E., Jhala, Y.V., Raghavan, B., Rahmani, A.R., Cuthbert, R., Pain, D.J., Meharg, A.A. (2007). Diclofenac residues in carcasses of domestic ungulates available to vultures in india. Environmental Internatl. 33, 759-765.
Swan, G., Naidoo, V., Cuthbert, R., Green, R.E., Pain, D.J., Swarup, D., Prakash, V., Taggart, M., Bekker, L., Das, D., Diekmann, J., Diekmann, M., Killian, E., Meharg, A., Patra, R.C., Saini, M., Wolter, K. (2006). Removing the Threat of Diclofenac to Critically Endangered Asian Vultures. PLoS Biology, 4(3), e66. DOI: 10.1371/journal.pbio.0040066