Date of Graduation

12-2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Poultry Science (PhD)

Degree Level

Graduate

Department

Poultry Science

Advisor/Mentor

Rochell, Samuel J.

Committee Member

Coon, Craig N.

Second Committee Member

Kidd, Michael T.

Keywords

calcium; corn fermented protein; phosphorus; phytic acid; precision-fed rooster; secretory IgA

Abstract

The availability of P in feedstuffs and the effect of feedstuffs, feed additives, and anti-nutritional factors on secretory IgA (sIgA) production in chickens were evaluated. A rapid method was developed using the precision-fed rooster assay to evaluate phytic acid disappearance, P digestibility, and phytase efficacy. Further, exogenous phytase was found to be effective at degrading myo-inositol 1,2,3,4,5,6-hexakis, however, the enzyme was less efficient at P release from lower inositol phosphates. The availability of P in feedstuffs was found to be affected by dietary Ca content, where increasing Ca linearly reduced (P < 0.05) both phytic acid hydrolysis and P digestibility. For example, the standardized ileal digestibility of P was reduced from 73 to 47% in soybean meal when the dietary Ca content was increased from 0.30 to 0.75%. The digestibility of P in distillers dried grains with solubles (DDGS) and corn fermented protein (CFP), however, was high across all Ca levels (71 to 80%). Relative P bioavailability based on tibia bone ash was also found to be high for DDGS and CFP, being 81 and 78%, respectively. Upon further evaluation, it was observed that utilizing low dietary Ca levels (0.30%) when P digestibility in individual plant-based feedstuffs was determined overestimated the P digestibility in practical grower diets by up to 16 percentage units. Utilization of higher Ca levels (0.75%) when P digestibility in individual plant-based feedstuffs was determined, however, resulted in calcualted P digestibility values that were within 1 to 3 percentage units of the measured digestibility in practical grower diets. Aside from P, feedstuffs were also evaluated to determine their effect on sIgA production in the intestine. Roosters excreted approximately 6 to 30 mg of sIgA / 24 h. Further, the proportional contribution of sIgA to total endogenous amino acid (AA) losses ranged from 1 to 13%, with the greatest contribution being observed for Trp. The addition of casein to a protein-free diet increased (P < 0.05) sIgA production in both roosters and broiler chickens. There was no change (P > 0.05) in sIgA production compared with the protein-free diet when the same amino acids (AA) were added in purified form; therefore, this effect was unique to the intact protein source. A variety of feedstuffs, feed additives, and anti-nutritional factors were also evaluated to determine their effect on sIgA production. Raw soybeans reduced (P < 0.05) ileal and excreta sIgA concentrations and total sIgA excretion (mg / 24 h). Feeding DDGS and CFP were also found to result in lower (P < 0.05) sIgA concentrations in excreta. Results from these studies demonstrate that 1) phytic acid disappearance in precision-fed roosters can provide preliminary estimates of P digestibility in plant-based feedstuffs, 2) utilization of low dietary Ca levels in when determining P digestibility in individual plant-based feedstuffs overestimates P digestibility in commercially relevant diets due to reduced hydrolysis of phytic acid as Ca content increases, and 3) feedstuffs and other dietary components can regulate sIgA production in the gastrointestinal tract through host-diet interactions.

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