Ruminant Nutrition: Beef - Minerals & Vitamins

The effect of vitamin D source and time of feeding 25-OH vitamin D3 (HyD r ) on broiler production efficiency and carcass composition was studied. The first hydroxylation of vitamin D in the liver results in 25-OH vitamin D3 (25-OHD3); providing dietary 25-OHD3 to the bird reduces the need for this hydroxylation, potentially allowing for a more efficient use of vitamin D. The dietary treatments differed only in supplemental vitamin D source: the Control diet contained 3,000 IU/kg of vitamin D3, the 25-OHD3 diet contained 69 μg/kg of 25-OHD3. Four dietary treatments were fed: Control (Control diet from 1-41 d), 25-OHD3 (25-OHD3 diet from 1-41 d), 25-OHD3 Early (25-OHD3 diet from 1-28 d, Control diet from 29-41 d), or 25-OHD3 Late (Control diet from 128 d, 25-OHD3 diet from 29-41 d). Birds were reared sex separately in 32 pens, with 4 replicates per treatment within each sex. Feed consumption and BW were measured at 0, 10, 28 and 41 d. At 42 d, 80 birds from each male pen were randomly selected for carcass and portion yield analysis. Birds in the 25-OHD3 and 25-OHD3 Early groups had a greater BW gain than the Control and 25-OHD3 Late groups from 11-28 d, gaining 55 and 55 vs 53 and 53g·bird-1·d-1, respectively (P<0.05). By 42 d, birds fed the 25-OHD3 treatment were heavier than those fed the Control and 25-OHD3 Late treatments (2301 vs 2233 and 2234 g, respectively; P<0.05). All treatment groups maintained similar feed conversion efficiencies (P>0.05). Starved and eviscerated BW and absolute weight of the pectoralis major, wings and drums were greater for the 25-OHD3 fed birds than those fed the Control and 25-OHD3 Late treatments (P<0.05). Overall, the 25-OHD3 treatment supported a faster BW gain, and greater breast and leg portions. All groups in this study developed field rickets around 11 d, however symptoms subsided and no treatment was administered. The results of this study are therefore confounded by the rickets, but may indicate that 25-OHD3 helped to lessen the effects of rickets as shown by the greater growth rate.