Reducing the cost of beef production through genetic improvement in residual feed intake: Opportunity and challenges to application 1

There is considerable individual animal variation in feed intake above and below that expected or predicted on the basis of size and growth rate. This difference in intake is calculated as residual (or net) feed intake (RFI). Genetic variation in RFI of beef cattle exists both during growth (slaughter generation and replacement females; heritability estimates since 1996 range from 0.16 to 0.43) and in adult cattle (the breeding herd; the one published heritability estimate is 0.23). Evidence shows that selection for lower RFI measured postweaning will lead to a decrease in feed intake by young cattle and by cows, with no compromise in growth performance or increase in cow size. Results from a single generation of divergent selection on postweaning RFI between 8 to 12 mo of age demonstrated favorable correlated changes in average daily feed intake (9.2 ± 0.2 vs. 9.8 ± 0.2 kg/d), RFI (−0.20 ± 0.11 vs. 0.17 ± 0.10 kg/d), and feed:gain ratio (F:G; 7.0 ± 0.2 vs. 7.6 ± 0.2 kg/kg) in Angus feedlot steers. In Angus cattle, the genetic correlation between postweaning RFI with av- erage daily feed intake by the cow is high (0.64), and