COMPARISON OF DIETARY 25-HYDROXYCHOLECALCIFEROL AND CHOLECALCIFEROL IN BROILER-CHICKENS

We conducted a series of 10 feeding trials involving over 36,000 broil ers. The effects of various dietary levels of cholecalciferol (vitamin DB) or 25-hydroxycholecalciferol (25-OH-D-3) were compared using a '' basal'' dosage level of 69 mu g/kg feed, as well as levels ranging fro m .5 to 1.5 times the basal level. For all 10 studies, average body we ight increased by an average of .042 +/- .03 kg (P <.001) and adjusted feed efficiency decreased (improved) by an average of .026 +/- .0046 kg/kg (P <.001) in birds fed 25-OH-D-3 in comparison to those fed vita min D-3 at the basal level. Changes in mortality were not detected. Ev aluation of different dietary levels of 25-OH-D-3 revealed a significa nt dose-response relationship, with maximal effects on weight gain, fe ed efficiency, and breast meat yield being observed in the range of 50 to 70 mu g/kg feed. Preliminary studies with different levels of vita min D-3 suggested no additional benefits on weight gain or feed effici ency with higher dietary levels of vitamin D-3. Serum 25-OH-D-3 concen trations increased more rapidly in birds fed 25-OH-D-3 than in birds f ed vitamin D-3 There were significant correlations with body weight, f eed conversion, and serum 25-OH-D-3 concentrations, with no correlatio ns observed between serum 1,25-(OH)(2)D-3 concentrations and these var iables.