Safety of 25-hydroxyvitamin D3 as a source of vitamin D3 in layer poultry feed
Terry, M.; Lanenga, M.; McNaughton, J.L.; Stark, L.E.
Veterinary and Human Toxicology 41(5): 312-316
1999
ISSN/ISBN: 0145-6296 PMID: 10509435 Document Number: 505443
The effects of providing 25-hydroxyvitamin D3 (25-OH-D3) in laying hen diets at levels ranging from 0.5 to 10 times the level commonly used for vitamin D3 supplementation in the poultry industry, were investigated. Following a 28-day preconditioning period, 5 groups of laying hens were fed commercial diets containing vitamin D3 68.9 micro g/kg feed (control) or 25-OH-D3 41.25 (0.5x), 82.5 (1x), 412.5 (5x), or 825 (10x) micro g/kg feed. The study compared the effects of the control level of vitamin D3 and the various test levels of 25-OH-D3 on health, performance, haematology, and 25-OH-D3 tissue concentrations in laying hens from 0 to 112 days of treatment and on health, performance, gross pathology and histopathology from 113 to 224 days of treatment. Gross pathological and histopathological examination of selected tissues after 224 days revealed no lesions attributable to vitamin D toxicity at any level. Concentrations of 25-OH-D3 in edible tissues at 112 days were similar for birds in the control and 1x groups. On the basis of all variables monitored, including body weight gain and feed conversion, the 10x level of 25-OH-D3 produced clear toxicity (but no mortality), the 5x level caused limited threshold toxicity, and the 1x level induced no toxicity. The results indicate that 25-OH-D3 is safe for use in laying hen feed as a source of vitamin D3 at 82.5 micro g/kg feed (1x), with a margin of safety of approximately 5x between the proposed 1x level and the 5x level (412.5 micro g/kg feed) that constitutes threshold toxicity in layers.