Evaluation of the Dietary Vitamin D₃ Requirement of Modern Broiler Chickens and Partial Replacement of Vitamin D₃ With 25 Hydroxycholecalciferol

Abstract

The goal of this dissertation was to explore the response of broiler chickens to dietary D₃ (vitamin D₃) and 25-OH-D₃ (25-hydroxycholecalciferol) as well as to establish a protocol that precisely estimated the D₃ requirement of modern meat-type chickens through an oral gavage bioassay. For this purpose, three research projects were conducted. For the first and second experiments, broiler chickens were fed a diet devoid of D₃ for 21 d. The first 9 d of the study served to deplete the maternal stores of D₃. On d-10 of the study, a crystalline source of D₃ was diluted in corn oil to prepare graded levels of D₃ that were directly gavaged into the crop of birds for 11 d. Broken-line regression was employed to estimate the requirement of D₃ for maximum bone mineralization. The first experiment fed a mash corn-soy diet with reduced calcium and non-phytate phosphorus. The second experiment fed a corn-soy diet as well but as crumbles, and all nutrients met or exceeded industry-type nutritional requirements. The D₃ requirement of starter broilers was estimated in experiment-1 to be close to the 500 IU/kg of feed and in experiment-2 to be around 200 IU/kg of feed for maximum bone mineralization. I concluded that nutrient restrictions increased the D₃ requirement with respect the NRC (1994), and that maternal D₃ stores in the yolk highly influenced the growth performance and bone mineralization response of broiler chickens to dietary D₃. Using industry-type nutritionally adequate diets, the dietary D₃ requirement appears to be in agreement with the NRC (1994).

In the third experiment, broiler chickens were subjected to a coccidiosis vaccine challenge and fed dietary concentrations of D₃ or a partial replacement of D₃ with 25-OH-D₃. Results suggested that the combination of both D₃ and 25-OH-D₃ was more effective than D₃ alone in promoting bone mineralization and enhancing vitamin D status as measured by total plasma 25-OH-D₃ in young (21 d-old) broiler chickens. Additionally, the supplementation of high dietary levels of D₃, independently of the source, above NRC (1994) recommendations, yielded better performance, bone mineralization and total plasma 25-OH-D₃ in starter broiler chickens.