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* The Cooperative Research Centre for Cattle and Beef Quality NSW Agriculture, Beef Industry Centre, Armidale, NSW 2351 Australia and
and
NSW Agriculture, Agricultural Research Centre, Trangie, NSW 2823 Australia
2 Correspondence: phone: 61 2 6770 1808; fax: 61 2 6770 1830; E-mail: robert.herd{at}agric.nsw.gov.au.
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 average daily feed intake by the cow is high (0.64), and the correlation between postweaning RFI and cow RFI is very high (0.98); however, the correlation between postweaning RFI and cow F:G is low (–0.06). These genetic correlations indicate that selection against postweaning RFI has the potential to lead to a decrease in feed intake and improvement in feed efficiency of growing animals and mature animals. Measurement of feed intake might occur in central test stations, or on-farm, and uniform guidelines are required to ensure that standardized and accurate data are generated. Ways of utilizing information generated in genetic evaluations are discussed. An EBV for feed intake after a phenotypic adjustment for growth performance (growth rate and BW) seems most practical. Such EBV would best be used in an economic selection index to account for genetic correlations with other traits in the breeding objective, including feed intake of the breeding herd, and the economic value of feed in relation to other traits. Further research is needed to examine these genetic relationships and to find ways for cost-effective identification of superior cattle.
Key Words: Beef Cattle • Feed Intake • Genetic Correlation • Heritability • Selection
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