Abstract
Variation in residual feed intake, that is, variation in feed intake in relation to liveweight (LW) and growth rate, was investigated using data from 540 progeny of 154 British Hereford sires, collected over ten 200-day postweaning performance tests conducted between 1979 and 1988. Residual feed intake (RFI Reg) was calculated for each test as the difference between actual feed and expected feed intake predicted from a multiple regression of feed intake on metabolic mid-test LW and average daily gain (ADG). RFI Reg was heritable (0.16, S.E. 0.08) and phenotypically and genetically independent of size and growth rate. RFI Reg had favourable phenotypic and genetic correlations with feed conversion ratio (FCR) and estimated maintenance energy expenditure. It was negatively correlated with estimated lean content of the carcase (LEAN) and appeared to be genetically independent of mature cow LW (COWWT). RFI Reg over the performance test was not affected by differences in pre-test rearing treatments, in contrast to start-of-test LW and end-of-test LW, and in some years, ADG and FCR. Selection against RFI has the potential to increase the efficiency of beef production by reducing feed intake without changing the growth rate of the young animal, or increasing mature cow size.
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