Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Wamsley, Kelley

Committee Member

Boltz, Timothy

Committee Member

Macklin, Kenneth

Committee Member

Pacheco, Wilmer

Committee Member

Rochell, Samuel

Date of Degree

8-12-2026

Original embargo terms

Visible MSU Only 1 year

Document Type

Dissertation - Campus Access Only

Major

Agricultural Science (Poultry Science)

Degree Name

Doctor of Philosophy (Ph.D.)

College

College of Agriculture and Life Sciences

Department

Department of Poultry Science

Abstract

Corn is the primary ingredient in broiler diets, and its particle size (CPS; feed microstructure) along with the physical quality of the finished feed (FQ; feed macrostructure) have independent effects on performance yet their combined, phase-specific optimization has received limited attention. The objective of this research was to evaluate CPS and FQ combinations across the starter, grower, and finisher phases of male Ross YP x Ross 708 broilers, with and without a subclinical enteric challenge (SEC). In the first study (Chapter II), broilers received treatments based on a 3 x 3 factorial of CPS [low (LCPS; 600 microns), medium (MCPS; 900 microns), high (HCPS; 1,200 microns)] and crumble FQ [low (LFQ; 1,600 microns), medium (MFQ; 2,400 microns), high (HFQ; 3,200 microns)] during the starter phase (d 0-17) with a 10x live coccidiosis vaccine challenge. Early body weight was negatively impacted by HCPS and HFQ; however, by d 17 the most consistent performance was observed in birds fed MCPS combined with HFQ. In the second study (Chapter III), all birds received the optimized starter diet (MCPS + HFQ) as a pretest (d 0-17), then were evaluated across grower-phase (d 17-28) CPS and FQ combinations in both an unchallenged (EXP1) and SEC (EXP2) experiment. In EXP1, MCPS improved FCR by approximately 6-8 points versus LCPS and HCPS, and HFQ numerically improved growth beyond other FQ levels. No CPS or FQ differences were detected in EXP2. In the third study (Chapter IV), the finisher phase (d 27-35) was evaluated using the same factorial design across two simultaneous experiments. In EXP1, MCPS and HCPS improved body weight versus LCPS; at processing, HFQ maximized carcass, breast, and total breast weight versus lower FQ levels. In EXP2, HFQ improved finisher gain and FCR regardless of CPS. Across both experiments, HFQ consistently supported performance and processing outcomes. Collectively, these data support a phase-feeding strategy that prioritizes MCPS (~900 microns) and HFQ across the broiler growout, with FQ representing the driver of performance particularly under enteric disease.

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