Safety of 25-hydroxyvitamin D-3 as a source of vitamin D-3 in layer poultry feed

A target animal safety study investigated the effects of providing 25-hydro xyvitamin D-3 (25-OH-D-3) in laying hen feed at levels ranging from 0.5 to 10 times the level commonly used for vitamin D-3 supplementation in the pou ltry industry. Following a 28-day preconditioning period, 5 groups of layin g hens were fed commercial diets containing 68.9 mu g of vitamin D-3/kg fee d (control) or 41.25 (0.5x), 82.5 (1x), 412.5 (5x), or 825 (10x) mu g of 25 -OH-D-3/kg feed. The study compared the effects of the control level of vit amin D3 and the various test levels of 25-OH-D-3 on health, performance, he matology, and 25-OH-D-3 tissue concentrations in laying hens from 0 to 112 d of treatment and on health, performance, gross pathology and histopatholo gy from 113 to 224 d of treatment. Gross pathologic and histopathologic exa mination of selected tissues after 224 d revealed no lesions attributable t o vitamin D toxicity at any level of test material. Concentrations of 25-OH -D-3 in edible tissues at 112 d were similar for birds in the control and 1 x groups. On the basis of all variables monitored, including body weight ga in and feed conversion, the 10x level of 25-OH-D-3 produced clear toxicity (but no mortality), the 5x level caused limited threshold toxicity, and the 1x level induced no toxicity. These results indicate that 25-OH-D-3 is saf e for use in laying hen feed as a source of vitamin D-3 at 82.5 mu g/kg fee d (1x), with a margin of safety of approximately 5x between the proposed Ix level and the 5x level (412.5 mu g/kg feed) that constitutes threshold tox icity in layers.