Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Animal Science

First Advisor

Michael E. Persia


The objective of this dissertation was to evaluate the effects of exogenous enzymes (EE) and direct-fed microbial (DFM) supplementation on bird 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 performance of laying hens when fed a diet with 100 kcal/kg reduced ME 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 gene expression and reduced zoonotic pathogen colonization. These data indicate that modern laying hens have little or no sensitivity to small differences in dietary ME contributed by EE and DFM, 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. Ileal nutrient transport, mucin gene expression and intestinal epithelial barrier function and were increased by DFM, although no difference in performance was observed. The effects of EE and DFM on dietary energy utilization in broilers were determined in two experiments. Both additives increased apparent ileal starch and amino acid 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 the birds were in a positive energy state. Changes in body composition indicated that the combination tends to increase lean accretion during early stages of life. Overall, the combination of EE and DFM increased broiler performance additively through pathways independent of each other.

Copyright Owner

Ganapathi Raj Murugesan



File Format


File Size

176 pages