Potential for selection to improve efficiency of feed use in beef cattle: a review

Evidence for genetic variation in feed efficiency of beef cattle is reviewe d in this paper, and ways in which this variation might be used in selectio n programs to improve beef cattle in Australia are discussed. Efficiency of beef production systems is determined by feed and other inputs of all clas ses of animals in the production system as well as outputs in terms of slau ghter progeny and cull cows. Different indices have been used to express as pects of efficiency on cattle over certain periods of the production cycle. Use of these indices is discussed, and then evidence for genetic variation in both growing animals and mature animals is reviewed. Genetic variation in feed efficiency exists in both growing and mature cattle, although infor mation is lacking to determine whether variation in total production system efficiency exists. The physiological basis for observed variation in feed efficiency is discussed, with differences in requirements for maintenance, body composition, proportions of visceral organs, level of physical activit y, and digestion efficiency identified as possible sources of variation. Selection to improve efficiency might be achieved by measuring feed intake of growing animals and utilising genetic correlations that are likely to ex ist between efficiency of growing animals and mature animals. Measurement o f feed intake might occur in central test stations, or methods may be devel oped to measure feed intake on-farm. Ways of utilising information generate d in genetic evaluations are discussed, and it is concluded that estimated breeding values for feed intake after a phenotypic adjustment for growth pe rformance would be most practical, although not theoretically optimal. Such estimated breeding values would best be used in an economic selection inde x to account for genetic correlations with other traits, including feed int ake of the breeding herd, and the economic value of feed in relation to oth er traits. Future research should be directed towards understanding the gen etic relationships between feed intake and other traits in the breeding obj ective, and to find ways to reduce the cost of measurement of feed intake, including a search for genetic markers.