Horses react more strongly to an excessive selenium exposure than cows or pigs. Intoxication causes are usually selenium-rich feed or water (more common in the USA or Canada then in Europe).
Symptoms of a chronic exposure and intoxication, referred to as 'alkali disease', are loss of long hair, hoof changes and a generally fatigued appearance. Symptoms of a subacute intoxication, called 'blind stagger', are ataxia and vision problems. The acute form of intoxication is the selenosis, which can cause cardiac insufficiency and sudden death.
Other symptoms of a selenium overexposure are weight loss, colic or diarrhea, problems swallowing, garlic-smelling breath, walking problems with a typical stiff gait.
Fur analysis can detect chronic overexposure. Blood testing reveals if the overexposure is immediate.