Lead (Pb):
Toxic metallic element found in old paint and caulking compounds, car batteries, lead pipes, lead headed nails, solder, places where lead painted timber was burnt, pasture downwind of lead smelters, pasture contaminated by dust from lead ore trucking. Lead bullets do not normally cause poisoning.
Lead is poorly absorbed but binds to red blood cells and spreads through the body, accumulating in liver, lungs, kidney, brain, bones, and teeth. It can enter the foetus and milk.
Lead is toxic in several ways, interfering with enzyme systems and replacing calcium and zinc. It has several effects on the nervous system interfering with neurotransmitters and hormones as well as haemoglobin manufacture.
Acute poisoning causes gastro-intestinal signs as well as neurological symptoms. Loss of appetite is usual along with mild colic. Neurological signs include blindness, head pressing, depression, abnormal gait, and sometimes seizures. Chronic poisoning signs may be subtle and difficult to diagnose and include laryngeal paralysis leading to “roaring” on inspiration.
Diagnosis is by clinical signs and blood testing for serum lead levels. Treatment includes seizure control and use of Calcium EDTA to chelate the lead and enable excretion coupled with supportive treatment. The source of the lead should be identified and removed. Where lead dust from ore is suspected the horse should be thoroughly washed.