ENVIRONMENT AND HEALTH Toxicity of a Vitamin D Steroid to Laying Hens1

ABSTRACT Two experiments were conducted with 56-week-old or 104-week-old Leghorn hens to determine if feeding vitamin D steroids in excess of requirement levels caused any marked affects on eggshell quality. In_the first experiment caged hens had reduced feed consumption, egg shelLqualitv. and egg production as early as 6 weeks after initially_cj)nsuming_a basaldiet supple-mented with 6.8 Mg la-hydroxvcholecalciferol (la-5H-D,)/kg. The second experiment confirmed the previous results and showed that extensive weight loss occurred with continued feeding of 10 or 15 Mg la-OH-D,/kg diet. No adverse affects were observed in either experiment when the level of la-OH-D3 supplementation was 5.0jig/kg diet or less. No toxic effects were observed when the hormone precurser 25-OH-D3 was supplemented to diets at 6 or 12 Mg/kg. It is suggested that the pathological effects observed are related to the potent calcium homeostatic properties of la-OH-D3 that at elevated levels may cause aberrations in circulating calcium. (Key words: vitamin D steroids, toxicity, hens)