Characterization of the effects of intestinal physiology modified by exogenous enzymes and direct-fed microbial on intestinal integrity, energy metabolism, body composition and performance of laying hens and broiler chickens

The objective of this dissertation research was to characterize the effects of intestinal physiology modulated by dietary supplementation of EE and DFM on intestinal integrity, energy metabolism, body composition and performance of laying hens and broiler chickens. The effects of reduced dietary metabolizable energy (ME) on performance, intestinal integrity and body composition of laying hens were evaluated in two experiments. A reduction of 90 kcal/kg of dietary ME over a period of 12 weeks did not significantly alter performance or nitrogen corrected apparent ME (AMEn), but reduced abdominal fat pad. In the follow-up experiment, no significant differences were noted in the performance of laying hens when fed a 100 kcal/kg reduced ME diet supplemented with EE or EE and DFM for 16 weeks. However, EE significantly increased AMEn and nutrient transport, whereas DFM increased intestinal epithelial barrier function, mucin expression and reduced zoonotic pathogen colonization. These data indicate that modern laying hens have little or no sensitivity to small differences in dietary ME, as they prioritize to meet the energy demands of production. The effects of DFM on performance and intestinal integrity of broiler chickens exposed to coccidial challenge or raised on built-up litter were evaluated. Ileal nutrient transport, mucin expression and intestinal epithelial barrier function were increased by DFM, although the performance was not altered. The effects of EE and DFM on dietary energy utilization in broilers were determined in two experiments. Both additives increased apparent ileal starch, amino acid and crude protein digestibility non-additively, while the combination additively increased AMEn. The effects of EE were exerted through increased activity of brush border digestive enzymes, and DFM through increased cecal butyrate synthesis. The final experiment examined the effects of EE and DFM on performance, energy utilization, and body composition in broiler chickens. The combination of EE and DFM additively increased feed efficiency and positive energy balance of chicks. Changes in body composition indicated that the combination tends to increase lean accretion during early stages of life overcoming the immaturity of digestive tract. Overall, the combination of EE and DFM increased broiler performance additively through pathways independent of each other.