Secondary Poisoning in Vultures

Secondary poisoning occurs when an animal consumes toxic residues present in another animal rather than encountering the toxicant directly. In vultures, residues of veterinary non-steroidal anti-inflammatory drugs (NSAIDs) in livestock carcasses can produce fatal poisoning after scavenging.

Pathway of exposure

Livestock may retain an NSAID in their tissues if they die soon after veterinary treatment. Vultures feeding on such contaminated carcasses ingest the residue, particularly when consuming visceral tissues, making carrion the link between veterinary drug use and wildlife poisoning.

• A single carcass may feed several vultures, so one contaminated animal can expose multiple scavengers.
• The best-known cause is veterinary diclofenac, which is highly toxic to vultures.

Physiological mechanism

After ingestion, diclofenac causes severe kidney damage in susceptible vultures. The kidneys then fail to eliminate uric acid efficiently, causing its concentration in the blood to rise.

• Urate crystals accumulate on and within internal organs, producing visceral gout.
• Renal failure and associated metabolic disturbance can result in death within a short period after feeding.

Conservation response

Because vultures locate carcasses efficiently and often feed communally, contaminated livestock carcasses can cause mortality over a wide area. India prohibited veterinary use of diclofenac in 2006, while meloxicam has been identified as a safer veterinary alternative for vultures.

• Effective protection requires excluding toxic veterinary drugs from the livestock carcass food chain.
• Drug regulation, carcass-residue surveillance, veterinary awareness and safe feeding sites complement habitat and breeding measures.