871 Lipid Metabolism and Mitochondrial Energy Production Are Key Pathways Involved in Adipose Tissue of Cows Transitioning from Feed Restriction to Ad Libitum Diets

Feed costs account for over 70% of the annual expenditures in cow/calf production. The majority of the nutrients are used to support the cow's maintenance requirements, and substrate cycling has been identified as one of the major contributors toward this type of energy expenditure. The objective of this study was to determine if cows that differ in the efficiency of weight gain differ in the relative abundance of transcripts for enzymes associated with lipid turnover of subcutaneous adipose tissue. Mature cows were subjected to feed restriction followed by ad libitum feed. Adipose tissue from 12 cows with high (n = 6; ADG = 2 kg/d) and low gain (n = 6; ADG = 1 kg/d), based on performance during the ad libitum feeding period, was collected during restriction and during ad libitum studies and evaluated for transcriptome expression differences using the Affymetrix GeneChip Bovine 1.1 ST Array. Differentially expressed genes were identified using an unpaired 1-way ANOVA for each pair of condition groups. None of the differentially expressed genes from high- versus low-gain animals by diet (feed restriction or realimentation) passed correction for multiple testing. However, 496 genes were differentially expressed (corrected P < 0.05) for the high-gain animals compared over the 2 studies and 491 genes were differentially expressed among low-gain animals between studies. Of these gene lists, 144 genes were common for both groups of animals. Enriched pathways based on differentially expressed genes includes oxidative phosphorylation, mitochondrial dysfunction, and cholesterol biosynthesis pathways that were commonly associated with the high-gain animals between feed restriction and realimentation as well as with the low-gaining animals between the 2 time points. Specific to cows with greater gain were valine degradation and lipopolysaccharide/IL-1 mediated inhibition of retinoid X receptor function pathways. Genes involved in lipid metabolism, mitochondrial respiration, and oxidative phosphorylation pathways appear to be critical to mature cows during times of abundant feed after feed restriction. The USDA is an equal opportunity provider and employer.