TOXICOLOGIC EVALUATION OF A HIGH-SELENIUM HAY DIET IN CAPTIVE PRONGHORN ANTELOPE (ANTILOCAPRA-AMERICANA)

Five captive-raised pronghorn antelope (Antilocapra americana) were fe d an alfalfa-grass hay diet containing 15 ppm total dietary selenium ( Se) for 164 days. Four additional captive-raised pronghorns fed a simi lar diet containing approximately 0.3 ppm total dietary Se served as c ontrols. None of the pronghorns had clinical signs attributable to the high Se hay. Plasma Se increased more rapidly than blood Se concentra tions, from baseline concentrations (<0.15 g/ml) to >0.40 g/ml within the first 50 days on the high selenium diet, but thereafter declined t o approximately 0.30 mu g/ml. Mean primary antibody response to hen eg g albumin was less in pronghorn on Se hay. No significant gross or his tological lesions attributable to selenosis were found, nor was there any evidence of dystrophic hoof growth. The greatest Se tissue concent rations were found in liver and kidney (5.67 to 10.4 mu g/g and 2.36 t o 3.14 mu g/g, respectively) from experimental animals; liver and kidn ey from the controls contained considerably less (less than or equal t o 0.52 mu g/g and less than or equal to 0.61 mu g/g, respectively). Ex posure of pronghorns for more than 5 mo to a diet containing 15 ppm Se caused significant increases in plasma, liver and kidney Se concentra tions, in the absence of clinical disease or pathologic lesions due to selenosis. Based on these results, we propose that pronghorns are les s susceptible to selenosis than previously reported and that diagnosti c criteria for the disease should be modified.