CHARACTERIZATION OF PROTEIN SOURCES AND THEIR EFFECTS ON BROILER PERFORMANCE, DIGESTIVE TRACT MORPHOLOGY AND CAECAL FERMENTATION METABOLITES

Abstract

The goal of this thesis was to characterize protein sources and evaluate their effects on broiler performance, digestive tract morphology and caecal fermentation. Understanding the digestion kinetics of high protein ingredients is an important step in elucidating the impact protein sources have on poultry performance and health. An in vitro assay was used to characterize the digestion kinetics of feed ingredients fed to broilers. The assay predicted the rapidly, slowly and undigested protein fraction of a variety of ingredients, and their digestion rate and extent. Compared to corn distiller dried grain with solubles, soybean meal and fish meal crude protein (CP) was digested more rapidly and to a larger extent. The rate and extent of protein digestion in feed ingredients were also evaluated using broiler chickens, and further the ileal digesta CP was characterized. Protein sources varied in rate and extent of CP and amino acid (AA) digestibility, distal ileum digesta residual AA, and total and soluble CP content. Fish meal, corn gluten meal and soybean meal had similar CP and AA extent of digestion in vivo. Among the protein sources, fish meal had the highest digestion rate for most AA. The total and soluble CP in the distal ileal content of birds fed protein sources ranged from 54 to 1466 and 6 to 347 mg, respectively. When broilers were vaccinated for coccidiosis and fed antibiotic free diets, dietary protein level (PL) and the ratio of indigestible protein (IDP) fraction affected broiler performance and meat yield. The disease status of the birds and the level of digestible AA in the diets influenced the bird’s response to dietary IDP. The level of caecal metabolites depended on dietary protein source, disease status of the birds and PL. In conclusion, data generated on in vitro and in vivo protein digestion kinetics provide an opportunity to categorize feed ingredients and use this information to establish the impact of these characteristics on broiler nutrition. Dietary PL and IDP affected broiler performance and meat yield when birds were vaccinated for coccidiosis and this was related to the characteristics of the protein sources present in the diets.