Semester

Fall

Date of Graduation

2023

Document Type

Dissertation

Degree Type

PhD

College

Davis College of Agriculture, Natural Resources and Design

Department

Animal and Nutritional Sciences

Committee Chair

Ibukun M. Ogunade

Committee Member

Gene Felton

Committee Member

Jianbo Yao

Committee Member

Joseph Lynch

Committee Member

Matthew Wilson

Abstract

Efficient feed utilization is critical for both economic sustainability and environmental responsibility in modern livestock production. While there has been extensive research, the multifaceted nature of feed efficiency remains complex, with many biological factors still unexplored. This dissertation examines the physiological foundations of feed efficiency by elucidating some of the complex biological mechanisms associated with residual feed intake (RFI) phenotype in beef cattle, using a range of Omics approaches. We hypothesized that metabolites related to amino acids, carbohydrates, and fatty acids could act as potential biomarkers for RFI. Through a chemical group-based metabolomics method, we identified enriched pathways in feed-efficient steers, notably in arginine biosynthesis and histidine metabolism. This led to the identification of five potential metabolite biomarkers mainly linked to amino acid metabolism, emphasizing a relationship between blood amino acid profiles and RFI. This led us to investigate the expression of genes and associated pathways related to nutrient and energy metabolism, especially in liver tissue, where hepatic metabolism is driven by transcriptional regulation. Low-RFI steers showed upregulation of genes involved in fatty acid transport, β-oxidation, and mitochondrial ATP production. In contrast, a crucial gene in amino acid metabolism responsible for aminoadipate aminotransferase activity exhibited a significant decrease in expression in low-RFI steers. These results indicate that alteration in expression of hepatic genes regulating lipid and amino acid metabolism, and mitochondrial ATP generation is associated with RFI phenotype. We also investigated potential differences in the rumen microbiome and immune gene expression of beef steers with low or high RFI. We observed increased mRNA expression of immune-related genes in both blood and liver tissues of low-RFI beef steers, especially those linked to pathogen detection and phagocytosis. Low-RFI steers also displayed variation in the relative abundance of microbial taxa compared to high-RFI. Lastly, detailed statistical analysis indicated that plasma amino acids such as tyrosine, glycine, and dimethyl sulfone may be promising economic prospects as cost-efficient predictors of RFI in beef cattle. In conclusion, this dissertation provides invaluable insights into some of the intricate biological processes associated with RFI in crossbred beef cattle, enhancing our grasp of the involved biological mechanisms and laying the groundwork for refining feed utilization in the beef cattle sector of livestock production.

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