| dc.description.abstract | The studies in this dissertation were conducted to evaluate the response of modern broiler chickens to dietary D 3 and 25-OH-D 3 (25-hydroxycholecalciferol) as well as to establish a marginal vitamin-D-depleted broiler breeder flock to increase the sensitivity of the oral gavage bioassay establish previously in our laboratory.
In the first and second experiments, commercial broiler chickens were fed a diet devoid of D 3 for 17 and 21 d, respectively. The first 9 d of the study served as a depletion period of the maternal stores of D 3 . On d-10 through the end of each trial, birds were offered commercially available sources of vitamin D 3 or 25-OH-D 3 by gavage daily. The basal diets were formulated with sub-optimal levels of calcium and nonphytate phosphorus (0.75 and 0.375% respectively). Experiment 1 results indicated no significant performance differences between dietary supplementation of either vitamin D3 or 25-OH-D3 . However, significant (P<0.05) differences for body weight (BW) and weight gain (WG) between the negative control and treatment groups were observed. For experiment 2, no performance or bone mineralization differences were detected between treatment groups or the negative control. This suggests that maternal stores of D3 in the yolk were sufficient to last the broiler chicks through the duration of the trial.
In the third trial, a commercial breeder flock was marginally depleted of vitamin D in order to run a vitamin D requirement study on the progeny chicks. A negative control response was observed between all treatment groups and suggests that establishing a marginally vitamin-D-deficient breeder flock increases the sensitivity of establishing vitamin D requirements. Furthermore, this experiment estimated the vitamin D3 requirement to be 73 IU/kg of feed based on bone ash. Using industry-type diets as in this trial, the dietary D3 requirement appears to be lower than reported in the NRC (1994).
The last trial evaluated the vitamin D requirement of two modern broiler strains (Cobb-500 and Cobb-700) using the oral gavage intubation assay. Results from this study showed no significant differences in performance parameters, however, main effect differences between strains for all performance and bone mineralization parameters were observed. | |
