"Measures of feed efficiency in beef cattle: Biological basis and effec" by Modoluwamu Idowu

Author ORCID Identifier

https://orcid.org/0009-0002-8389-5374

Semester

Fall

Date of Graduation

2024

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

Matt Wilson

Committee Member

Jianbo Yao

Committee Member

Joe Moritz

Committee Member

Joseph Lynch

Abstract

During the feedlot receiving period, newly weaned beef cattle face various stressors, including weaning, transportation, vaccination, and exposure to pathogens. Additionally, changes in diet and low dry matter intake contribute to nutrient deficiencies, heightening susceptibility to disease and performance declines. Therefore, we examined the effects of dietary supplementation with a multicomponent blend of prebiotics and probiotics on the health, immune status, metabolism, and performance of newly weaned beef steers during a 35-day receiving period. Our results showed that compared to the control group, the supplemental additive (SYNB) increased average daily gain (ADG), dry matter intake, and meal events during the first 7 days. Over the entire 35-day receiving period, beef steers fed supplemental SYNB had greater ADG and feed efficiency and a lower percentage (35% vs. 50%) of animals treated for Bovine Respiratory Disease (BRD). Whole blood expression of pro-inflammatory genes was downregulated while that of anti-inflammatory genes was upregulated in beef steers fed supplemental SYNB. Six nutrient metabolic pathways associated with health benefits were enriched in beef steers fed supplemental SYNB. This study demonstrated that dietary supplementation of SYNB during the first 21 days of arrival reduced BRD morbidity, improved the performance, immune, and metabolic status of beef steers over a 35-day receiving period, thereby extending the SYNB effect by a further 14-day post-supplementation. However, due to inconsistent responses to supplemental microbial products and the development of new direct-fed microbial strains, there is a need for more research studies to provide insight into their mechanisms of action and the physiological factors affecting these responses. Therefore, in the second chapter of this dissertation, we employed a range of omics approaches to focus on elucidating the biological mechanisms associated with the divergent Residual Body Weight Gain (RADG) phenotype in beef cattle. Through ruminal and plasma metabolomics, as well as 16S rRNA gene sequencing, this dissertation aimed to identify differences in host metabolome, rumen metabolome, and microbial community in beef steers with positive or negative RADG phenotype. Our microbiome results revealed greater relative abundance of Bacteroidetes_vadinHA17 and Anaerovibrio in beef steers with positive RADG compared to the negative RADG group. Additionally, pathway enrichment analysis of the metabolome data revealed the enrichment of five metabolic pathways including steroid hormone biosynthesis, thiamine metabolism, and propanoate metabolism in the plasma of steers with positive RADG. Overall, our results showed that selection for divergent feed efficiency phenotype is associated with differences in rumen microbiome and overall animal metabolism, notably amino acid metabolism-related pathways, and therefore may be an important animal-related factor that can affect the response of beef cattle to nutritional interventions such as rumen bypass protein supplement. Feeding rumen-bypass protein to cattle has demonstrated positive impacts on weight gain and feed efficiency, especially in rapidly growing young calves. However, the increasing costs of feeding protein and the challenges of excessive nitrogen (N) discharge into the environment underscore the need for sustainable protein supplementation in ruminant diets. Although past research has aimed at enhancing amino acid utilization efficiency and/or reducing nitrogen excretion in ruminants by minimizing dietary protein content, there's a gap: no study has assessed how factors intrinsic to the animal, like feed efficiency status, might influence the response of ruminants to dietary protein supplements. In our follow-up study, we investigated the effects of a rumen-bypass protein (RBP) supplement on growth performance, plasma and urinary N concentration, hepatic mitochondrial protein complexes, and mRNA expression of immune genes in crossbred beef steers with divergent negative or positive residual feed intake (RFI) phenotype, another measure of feed efficiency. We assessed the impact of rumen by-pass protein (RBP) supplementation on feed efficiency in beef steers. Forty steers (BW: 492 ± 36 kg) underwent a 42-day trial in a 2 × 2 factorial arrangement, considering RFI classification and RBP supplementation. Liver tissue samples collected on day 42 were analyzed for mRNA expression of immune genes and mitochondrial protein complexes I - V. Regardless of RFI status, RBP increased blood urea nitrogen (BUN) (P = 0.01), with lower BUN in low-RFI steers. Interactions of RBP and RFI were observed (P ≤ 0.05) for mitochondrial activities of complexes IV, V, and mRNA expressions of immune genes (TLR2, TLR3, IL23A). While RBP did not impact growth performance, its effects on immune gene expression and mitochondrial protein complexes varied with RFI status, highlighting the importance of considering feed efficiency status in future studies investigating the effects of dietary protein supplements effects in beef cattle.

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