EFFICIENCY OF NUTRIENT USE IN CATTLE:IDENTIFICATION OF CRITICAL PHYSIOLOGIC AND GENOMIC REGULATORY PATHWAYS
Title: Enhanced mitochondrial complex gene function and reduced liver size may mediate improved feed efficiency of beef cattle during compensatory growth
Submitted to: Functional and Integrative Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 22, 2009
Publication Date: September 24, 2009
Citation: Connor, E.E., Kahl, S., Elsasser, T.H., Parker, J., Li, R.W., Van Tassell, C.P., Baldwin, R.L., Barao, S.M. 2009. Enhanced mitochondrial complex gene function and reduced liver size may mediate improved feed efficiency of beef cattle during compensatory growth. Functional and Integrative Genomics. 10(1):39-51.
Interpretive Summary: Compensatory growth following a period of imposed feed restriction is known to occur in ruminants and is associated with many physiological changes including increased feed efficiency. In order to identify genes that may be responsible for the improvement in feed efficiency during compensatory growth, gene expression in liver tissue of control (ad libitum fed) versus feed-restricted steers was compared at three time points-- after 10 weeks of feed restriction, after 1 day of ad libitum feeding following a 12-week period of feed restriction, and 14 days after ad libitum feeding following a 12-week period of feed restriction. Results of the study indicated similarities between cattle and mice in genetic responses to feed restriction. In addition, results suggested that an increase in mitochondrial function may be a mechanism by which animals exhibit improved feed efficiency during compensatory growth. Genes identified by this work will be the target of future investigations to aid in the identification and selection of animals that are inherently more efficient at feed conversion.
Growing ruminants maintained under dietary restriction for extended periods will exhibit compensatory growth when reverted to ad libitum feeding. This period of compensatory growth is associated with increased feed efficiency, lower basal energy requirements, and changes in circulating concentrations of metabolic hormones. To identify genetic mechanisms contributing to these physiological changes, 8 month-old steers were fed either ad libitum (control; n = 6) or 60-70% of intake of control animals (feed-restricted; n = 6) for a period of 12 weeks. All steers were then fed ad libitum for the remaining 8 weeks of the experiment (realimentation period). Liver was biopsied from each animal at days -14, +1 and +14 relative to realimentation for RNA extraction and gene expression analysis by microarray hybridization. During the first 14 days of realimentation, feed-restricted steers exhibited a greater rate of gain compared to controls and substantially greater feed efficiency. Associated with this period was an increase in expression of genes functioning in cellular metabolism, cholesterol biosynthesis, oxidative phosphorylation, glycolysis and gluconeogenesis. Of interest, there was no overlap in the identity of genes affected by realimentation at day +14 with those affected at day +1. Many observed changes in gene expression during the feed restriction period were similar to those reported in mice, indicating similar effects of caloric restriction across species. Based on substantial up regulation of expression of genes encoding the mitochondrial complex proteins, it was hypothesized that increased mitochondrial function may be a mechanism by which animals exhibit improved feed efficiency during compensatory growth.