Date of Graduation

12-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Poultry Science (PhD)

Degree Level

Graduate

Department

Poultry Science

Advisor/Mentor

Kidd, Michael

Committee Member

Parsons, Benjamin

Second Committee Member

Caldwell, David

Third Committee Member

Kegley, Elizabeth

Fourth Committee Member

Smith, Phillip

Keywords

Broiler; Energy; Gums; Lysine; Soap stocks; Soybean

Abstract

This dissertation explored strategies to optimize Cobb MX x 500 broiler chicken nutrition by investigating lysine and energy synergies, the utilization of soybean processing by-products (“add-backs”), and soybean genotype selection for enhanced amino acid composition. Three independent but complementary research objectives were pursued to improve feed efficiency, sustainability, and cost-effectiveness in modern broiler production. The first objective assessed the interactive effects of dietary lysine and metabolizable energy (ME) on the performance and carcass traits of Cobb MX × 500 broilers. Using a central composite design, nine dietary treatments were formulated across multiple feeding phases. Results demonstrated that broiler performance responded quadratically to both lysine and ME levels, indicating that optimal nutrient concentrations differed by growth phase and sex. These data highlight the need to continually update lysine and energy recommendations for contemporary broilers. The second objective examined the metabolizable and bioavailable energy of soybean gums and soap stocks and their potential as energy sources in broiler diets. Precision-fed rooster assays and broiler trials revealed that these lipid-based ingredients provided approximately 75–80% of the energy value of refined soybean oil (on a dry matter basis). Inclusion of up to 4% of these add-backs in soybean meal did not impair growth performance, feed conversion, carcass yield, or gut integrity, demonstrating their feasibility as low-cost energy supplements. The third objective evaluated soybean meal derived from an experimental soybean line bred for elevated amino acid concentrations, particularly noncommercially available amino acids (e.g., Phe, Tyr, Asp, Glu, Gly, Pro). Broilers fed diets containing this enhanced soybean meal exhibited comparable growth and yield to those receiving higher inclusions of conventional soybean meal, despite reduced soybean meal levels. Improved amino acid digestibility likely explained the maintained performance and reduced diet cost. Collectively, these findings demonstrate that optimizing lysine-to-energy ratios, incorporating soybean oil refining co-products, and using genetically improved soybean genotypes can enhance feed efficiency and nutrient utilization in broiler production, offering both economic and sustainability benefits for the poultry industry.

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