Investigation of Selenium Sources Associated with Chronic Selenosis in Horses of Western Iowa

Abstract

Chronic selenosis (alkali disease) was diagnosed in horses in the loess hills of western Iowa, 21 a region associated with marginal to adequate soil selenium and not previously reported to produce seleniferous crops. 6 Subsequent field investigations confirmed normal selenium levels in the soils sampled but elevated dietary intake. Locally produced seleniferous alfalfa hay (Medicago sativa L.) from 2 sites were identified as the primary sources. Drought-stimulated root development may have enabled long alfalfa taproots to extract selenium from deeper glacial subsoils. This communication describes the investigation of potential selenium sources associated with the horses and hays. Clinical signs of chronic selenosis began during the late summer of 1989 in 3 mares, 2 studs, and 2 yearlings at site A and 5 mares and geldings at site B. Affected horses all developed moderate to severe tail and mane alopecia. One stud (site A) had moderate corrugated hoof lesions on the forelimbs, and progressed to mild lameness. At site B, all horses reportedly developed hoof wall deformities and pronounced lameness. Prior to investigation, another horse had been euthanized because of pain, lameness, and hoof sloughing. All affected horses recovered after changing to lower selenium hay. During a previous drought in 1983, 3 mares on farm A developed signs compatible with chronic selenosis. Ranges of selenium concentration in samples (ppm wet weight), excluding site B, were hair coat, 0.30-7.1; mane hair, 055-1.0; tail hair, 0.55-1.0; blood, 0.44-1.1; serum, 0.280.49; hoof wall, 0.8-2.2; and hoof sole, 0.5-2.8. 21