Compared with vitamin A and vitamin D, in both acute and chronic studies with animals vitamin E has been shown to be relatively nontoxic, but not entirely devoid of undesirable effects. Hypervitaminosis E studies in rats, chicks and humans indicate maximum tolerable levels in the range of 1,000 to 2,000 IU per kg (455 to 910 IU per lb) of diet (NRC, 1987). For chickens the effects of vitamin E toxicity are depressed growth rate, reduced hematocrit, reticulocytosis, increased prothrombin time (corrected by injecting vitamin K) and reduced calcium and phosophorus in dry, fat-free bone ash (NRC, 1987).
An adverse effect of excessive intake of vitamin E is its interference with vitamin D utilization, particularly when the latter's dietary concentration is marginal. In broiler chickens, increasing dietary vitamin E adversely affected (P < 0.01) bone ash, plasma calcium, and plasma and liver vitamin A concentrations (Aburto and Britton, 1998a, b). Bartov (1997) concluded that vitamin E, at a concentration of 150 mg per kg (68.2 mg per lb) of diet, did not aggravate a mild vitamin D deficiency. It is important to formulate feed with the proper ratios of vitamins A, D3 and E.
