Effect of breed and dietary composition on the miRNA profile of beef steers divergent for feed efficiency

The aim of this study was to measure the effect of contrasting breed and dietary source on the skeletal muscle miRNA profile of beef cattle divergent for feed efficiency (RFI). Charolais (n=90) and Holstein-Fresian (N=77) steers) were offered two consecutive diets; namely a zero-grazed grass diet followed by a high concentrate diet. Dietary intakes were recorded for all steers throughout each dietary phase and residual feed intake values dertermined for each steer. At the end of each dietary phase the most efficient (Low-RFI; n=8) and least efficient (High-RFI; n=8) steers were selected across each breed for longissmus dorsi biopsy collection. RNA was isolated from all muscle tissue samples and subsequently used for small RNA sequencing. Ten miRNA were differentially expressed between the steers divergent for RFI across each diet and breed contrast. Biological pathway analyssi revealed enrichment of pathways related to both metabolic and growth processes. Overall design: In total 64 RNA samples were analysed, 8 from each High- or Low-RFI group across each breed and dietary phase. During the first dietary phase the steers received a zero grazed grass diet, whilst during the subsequent phase all steers received a high concentrate diet. Tissue samples were collected from the steers divergent for RFI within each breed at the end of each dietary phase.