Author ORCID Identifier

https://orcid.org/0009-0008-8570-2605

Semester

Spring

Date of Graduation

2026

Document Type

Dissertation

Degree Type

PhD

College

Davis College of Agriculture, Natural Resources and Design

Department

Animal and Nutritional Sciences

Committee Chair

Ibukun Ogunade

Committee Member

Scott Bowdridge

Committee Member

Jianbo Yao

Committee Member

Zaira Estrada

Abstract

Improving feed efficiency is a primary objective in livestock production, serving as a major driver of profitability and sustainability in beef cattle operations as feed costs continue to rise. Residual feed intake (RFI) and residual average daily gain (RADG) are widely recognized indicators of feed efficiency and are commonly used as selection traits to reduce production costs and environmental impact. Previous research suggests a functional shift in transcriptional activity associated with immunity depending on efficiency phenotype, with evidence of greater immune system robustness in more efficient animals. This dissertation examines the molecular mechanisms linking feed efficiency and immune competence and investigates whether feed-efficient cattle exhibit distinct immune activation patterns.

In the first study, we assessed whether Angus bulls with divergent RFI exhibited differences in immune gene expression. We identified five differentially expressed immune genes associated with pathways related to innate immune defense, cytokine regulation, LPS signaling, and cellular responses to bacteria, indicating notable differences in immune pathway regulation between groups with divergent efficiency phenotypes.

The second study examined changes in the PBMC transcriptome of beef steers with divergent RFI following in vitro LPS stimulation. Negative-RFI steers displayed a greater number of differentially expressed genes and enrichment of pathways related to inflammatory signaling and innate immune defense, suggesting a rapid and robust transcriptional reaction to LPS challenge. Positive-RFI steers showed fewer transcriptional changes, with enrichment of pathways associated with adaptive immune processes, suggesting a more balanced and energy-conserving immune activation strategy that may contribute to improved feed efficiency.

The third study investigated the effects of in vitro LPS stimulation on the PBMC transcriptome of beef steers with divergent RADG. While both groups exhibited similar transcriptional patterns in their initial reaction to LPS, differences emerged in the coordination of overall inflammatory transcriptional responses. Positive-RADG steers showed greater enrichment of pathways related to cytokine network activation, whereas negative-RADG steers demonstrated enrichment of pathways centered on IL-1 activation and regulation.

Collectively, this dissertation provides valuable insights into the molecular mechanisms underlying feed efficiency in beef cattle and how divergent efficiency phenotypes influence immune gene expression and inflammatory pathway regulation.

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