The effect of diet and breed on global gene expression profiles of animals divergent for RFI

The selection of cattle with high feed efficiency is of paramount importance with regard to reducing feed costs in the beef industry. Developing predictive biological markers specifically for improved feed efficiency is an attractive alternative to direct measurement on large numbers of animals.Evidence is provided that, effects of RFI on gene expression in muscle of beef cattle are not consistent across breed type or dietary phase. These novel observations challenge the practicality of selecting and breeding for low RFI animals across different diets and stages of development. Perhaps, future research should be directed at utilising different diets to harness the full genetic potential of animal based on breed or stage of maturity. Further to this, evidence is provided from our own work and that of others that less efficient HF steers consuming zero grazed grass are under increased stress as demonstrated by an upregulation of immune function in these animals. Residual feed intake was calculated in in Charolais (CH) and Holstein Freisan (HF) under ad libitum feeding conditions aross varying diets, which were subsequently ranked, within breed and diet, as high (n=12) or low (n=12) residual feed intake. RNA sequencing was performed on liver and skeletall muscle biopsies from high and low residual feed intake animals in order to identify differentially expressed genes that may be associated with this trait.