Date of Graduation


Document Type


Degree Name

Doctor of Philosophy in Poultry Science (PhD)

Degree Level



Poultry Science


Samuel Rochell

Committee Member

Sami Dridi

Second Committee Member

Billy Hargis

Third Committee Member

Audrey McElroy


Broiler, Coccidiosis, Digestibility, Nutrition, Vaccination


Four experiments were conducted to evaluate the interrelationships among coccidiosis vaccination and nutrient utilization in floor-reared broiler chickens. Experiment 1 longitudinally compared the effects of coccidiosis vaccination and a chemical coccidiostat on broiler performance, nutrient digestibility, and intestinal morphology. Coccidiosis vaccination had no significant impact on morphology, overall body weight gain and feed intake of vaccinated birds, although vaccination impaired overall FCR. Vaccination elicited a transient reduction in digestibility of energy and nutrients, particularly for lipids, but vaccinated birds were able to recover from these reductions by 20 d. Experiment 2 assessed the impact of vaccination in digestibility of different feed ingredients and consisted of a basal diet and 3 test diets in which 30% of the basal diet was replaced with either corn, soybean meal, or distillers dried grains with solubles to allow for calculation of nutrient digestibility of individual ingredients by difference. Vaccination negatively impacted ether extract digestibility, particularly for corn. Nutrient digestibility was minimally impacted by vaccination in birds fed soybean meal, whereas ether exact digestibility was minimally impacted and nitrogen and amino acid digestibility were improved by vaccination in birds fed distillers dried grains with solubles. In experiment 3, a fat-free diet was fed to determine the impact of a coccidiosis vaccination model on ileal endogenous fatty acid flow and the values obtained were used to standardize the ether extract and fatty acid digestibility values of birds fed soybean oil or poultry fat diets. The vaccine challenge model negatively impacted digestibility of ether extract and most FA, regardless of the dietary lipid source. However, these results suggest endogenous fatty acid losses account for much of the reduction in lipid digestibility. In experiment 4, the influence of 3 starter diet energy concentrations achieved with varying soybean oil supplementation on nutrient digestibility, growth performance and processing characteristics were evaluated in coccidiosis vaccinated broilers. Vaccination reduced nutrient digestibility in all diets but did not compromise overall body weight gain, feed intake, or most processing weights. However, vaccinated birds fed higher energy density diets through greater soybean oil supplementation during the starter period had impaired feed efficiency throughout the experiment.