Heavy metals in horses: A review of the toxicity, clinical consequences and expected safe tissue concentrations.

Trace elements arsenic, cadmium, lead, chromium, mercury, nickel, and zinc are high-density, naturally occurring metals notable for their toxicity and environmental persistence. Cadmium and mercury are particularly concerning due to their capacity for bioaccumulation and biomagnification within the food chain. Dispersed through both anthropogenic and natural sources, these elements pose significant threats to ecosystems and animal health. In equines, they induce oxidative stress by disrupting mitochondrial function, generating reactive oxygen species, and inhibiting antioxidant enzymes, leading to cellular damage and organ dysfunction. Clinical presentations including gastrointestinal, neurological, renal, and musculoskeletal disorders vary by element, dose, and exposure duration. This review compiles information on the origins, pathogenesis, clinical signs, and therapeutics for poisoning by these seven elements in horses. Additionally, literature-derived baseline levels in blood, serum, hair, liver, and kidneys are synthesized to propose preliminary species-specific reference values, supporting environmental monitoring, clinical diagnosis, and equine product safety.