CASE NOTES
Clinical presentations of lead poisoning
Bruce Watt, Central Tablelands Local Land Services, Bathurst
Posted Flock and Herd November 2024
Introduction
Worldwide, lead poisoning is one of the most common intoxications in cattle. Sheep are rarely affected. Young cattle are most susceptible because they are inquisitive and "lack oral discrimination" (Constable et al. 2017).
Lead is a toxin that affects the nervous, digestive, renal, hepatic, haematopoietic and reproductive systems. However, in my experience in cattle, clinical signs other than those associated with the nervous system are rare.
Presentations
Death
While cattle can die suddenly from lead poisoning, most present with neurological signs before they die. However, under extensive livestock grazing systems most stock are not observed daily so a common presentation is to find dead animals. Lead-affected cattle often walk, zombie-like, in one or more directions. Therefore, lead intoxication should be strongly suspected when cattle are found dead in unusual locations, such as in the wrong paddock, in a dam, tangled in a fence or caught in a tree. In my experience, poisoning usually occurs when cattle have gained access to a paddock or yard that normally isn't grazed, or when cattle access a paddock with recent changes such as earth moving.
Neurological
Lead-intoxicated cattle can present with a wide range of neurological signs including depression, ataxia, blindness, head pressing, muscle twitching, jaw champing and bruxism (Parkinson et al. 2019). While hyper-irritability, mania and aggression are reported, in my experience, cattle most commonly present as dull. Cattle that are normally alert and avoid close contact can become docile. Blindness is also a common presentation. Regular clonic contraction especially of cervical muscles is less common but is close to pathognomic. Rumen motility is reduced and tongue tone is low.
Gastrointestinal
Gastrointestinal tract dysfunction is reported to be common in lead-poisoned cattle with initial rumen atony and constipation followed by foetid diarrhoea (Constable et al. 2017). While I have noted ruminal atony I can't recall seeing foetid diarrhoea.
Recovering animals
I have seen several cattle clinically affected with neurological signs and markedly elevated blood levels that have survived and eventually recovered. Initially these cattle were dull, with a suppressed appetite and so suffered marked weight loss. They slowly recovered over 2-3 years.
References
- Parkinson TJ, Vermunt JJ, Malmo J and Laven R (2019) Diseases of Cattle in Australasia A comprehensive textbook. Second edition. Vetlearn
- Constable PD, Hinchcliff KW, Done SH and Grunberg W (2017) Veterinary Medicine - A textbook of the diseases of cattle, horses, sheep, pigs and goats. 11th Edition. Saunders publishing. Pages 1202-1208