Vitamin D3 requirements and relative bioavailability for starter male White Pekin ducks fed either cholecalciferol or 25-hydroxycholecalciferol

The objectives were to investigate effects of various concentrations of dietary vitamin D₃ (VD₃) or 25-hydroxycholecalciferol (25-OH-D₃) on growth performance, VD₃ status, calcium (Ca) metabolism, and tibia mineralization of starter male White Pekin ducks, and dietary requirements and relative bioavailability of these two compounds. One-day-old male White Pekin ducks (n = 624) were assigned to 13 dietary treatments, including 6 added VD₃ concentrations (100, 200, 400, 800, 1200, and 2000 IU/kg), and 2 vitamin D₃ sources (VD₃ and 25-OH-D₃), plus a negative control (no vitamin D₃ supplementation) for 21 days. Each group had 6 replicate pens of 8 birds per pen. At 21 days of age, growth performance, carcass traits, plasma 25-OH-D₃ and Ca content, and tibia mineralization were examined. There was a high incidence of leg disease and mortality in ducks fed the control diet; however, those negative effects were avoided by adequate VD₃ or 25-OH-D₃ supplementation. Ducks in the negative control group had the lowest body weight, average daily weight gain (ADG), average daily feed intake (ADFI), breast muscle percentage, plasma 25-OH-D₃, plasma Ca, and tibia indices (weight, diameter, ash, density, tibia mineral, strength) (P < 0.05), with all these end points enhanced linearly or quadratically as dietary VD₃ or 25-OH-D₃ increased (P < 0.05). Furthermore, at 100 or 200 IU/kg, ducks fed 25-OH-D₃ had greater body weight, ADG, ADFI, plasma Ca, plasma 25-OH-D₃, tibia weight, tibia diameter, tibia ash than those fed VD₃ (P < 0.05), indicating 25-OH-D₃ was more effective in stimulating growth, Ca absorption, and tibia mineralization. For growth performance, breast muscle percentage, plasma Ca, and tibial indices of starter male Pekin ducks, the VD₃ requirements were 281 to 633 IU/kg, whereas 25-OH-D₃ requirements were 119 to 395 IU/kg. Based on slope ratio comparisons from multiple linear regressions of plasma 25-OH-D₃, bioavailability of 25-OH-D₃ was 186% relative to cholecalciferol.