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Surface enlargement factor of rumen papillae and expression of genes involved in dermatological diseases and their relationships with feed intake in beef steers
Feed costs make up the largest portion of the total cost to produce beef. One way to reduce this cost, thereby increasing profitability of beef production, is to improve feed efficiency. The rumen is responsible for digestion and absorption of nutrients and microbial by-products and may play a significant role in feed efficiency of beef cattle. The objectives of this study were to determine if variation in rumen papillae morphology and dispersion plays a role in feed efficiency of beef steers, and to identify candidate genes for genetic markers of feed efficiency traits. Feed efficiency phenotypes were collected on a cross-bred population of steers. Steers were divided into four groups (2 × 2 factorial): high intake and high gain, low intake and low gain, high intake and low gain, low intake and high gain. Four of the most extreme steers from each group were selected for harvest (n=16). Rumen wall samples were taken from three locations in the rumen. Length and width were measured on 30 papillae from each sample site using digital calipers, and papillae density was counted for one square centimeter of each sample. Surface enlargement factor was also calculated for each rumen sample site, and was found to vary with feed intake (P = 0.04). Length, width, and density were not found to vary with feed efficiency traits (P > 0.12). RNA was extracted from papillae from the caudal ventral sac, and transcripts were sequenced to assess gene expression. Sequences were aligned to the annotated reference genome. Eight genes were differentially expressed between high and low gain, and fifteen between high and low intake (False Discovery Rate < 0.05). Genes identified were validated against either or both expression values or expression patterns identified by association using quantitative real-time PCR (P < 0.1). One gene associated with gain and nine genes associated with feed intake validated. Pathway analysis of genes associated with feed intake revealed a pathway related to dermatological diseases, conditions and inflammation. Several genes (CYP1A2, MYL1, KLK10 and KLK12) were previously associated with either feed efficiency traits or important ruminal functions. These data indicate that there is a relationship between the surface enlargement factor and feed intake, and that genes involved in epithelial disease and inflammation in rumen papillae are differentially expressed in animals with extreme feed intake phenotypes.
Keywords: Feed Efficiency RNA-Seq