Toxicity of a vitamin D steroid to laying hens

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 shell quality, and egg production as early as 6 weeks after initially consuming a basal diet supplemented with 6.8 micrograms 1 alpha-hydroxycholecalciferol (1 alpha-OH-D3)/kg. The second experiment confirmed the previous results and showed that extensive weight loss occurred with continued feeding of 10 or 15 micrograms 1 alpha-OH-D3/kg diet. No adverse affects were observed in either experiment when the level of 1 alpha-OH-D3 supplementation was 5.0 micrograms/kg diet or less. No toxic effects were observed when the hormone precursor 25-OH-D3 was supplemented to diets at 6 or 12 micrograms/kg. It is suggested that the pathological effects observed are related to the potent calcium homeostatic properties of 1 alpha-OH-D3 that at elevated levels may cause aberrations in circulating calcium.