Safety evaluation of dietary levels of 25-hydroxyvitamin D3 in growing calves.

The objective of this study was to evaluate the safety of 25-OH-D3 addition to the diet of bovine calves. The investigation was conducted as a feeding experiment for 90 days. 40 calves were allotted to four groups: T1 - control group which received 30 IU vitamin D3/kg feed, and three experimental groups, which received 25-OH-D3 in increasing dosages: T2 - 25-OH-D3 at 1.7 µg/kg, T3 - 25-OH-D3 at 5.1 µg/kg and T4 - 25-OH-D3 at 8.5 µg/kg. All calves in the four groups gained weight continually: no growth depression was observed. No adverse effects of 25- OH-D3 were observed for any of the hematology and serum chemistry parameters measured or during the routine clinical examinations. Plasma 25-OH-D3 concentration was higher (p<0.05) in groups T2, T3 and T4 compared to that observed in group T1. Tissues content of 25-OH-D3 was significantly higher in in groups T2, T3 and T4 than in group T1. In the post-mortem evaluation, no adverse effects of the different 25-OH-D3 doses were observed, neither during the gross pathology nor in the histological examination. The results of this study show explicitly that there were no adverse effects of 25-OH-D3 compared to the control group, supplemented with vitamin D3.