OPTIMUM POSTWEANING TEST FOR MEASUREMENT OF GROWTH-RATE, FEED-INTAKE,AND FEED-EFFICIENCY IN BRITISH BREED CATTLE

The optimum duration of test for measurement of growth rate, feed inta ke, feed conversion, and residual feed intake was examined using postw eaning feed intake and weight data from 760 Angus, Hereford, Polled He reford, and Shorthorn heifer and Angus bull progeny from 78 sires. Var iance components, heritability, phenotypic and genetic correlations, a nd the efficiency of selection using shortened tests compared with a 1 19-d test were used as criteria to assess the optimum test length. The results indicated that a 35-d test was sufficient for measurement of feed intake, whereas a 70-d test was required to measure growth rate, feed conversion, and residual feed intake without compromising the acc uracy of measurement, When a 70-d test is used to measure growth rate, feed conversion, and residual feed intake there is minimal loss in ac curacy when weights are collected every 2 wk instead of weekly, but a further increase in the interval between weights to 5 wk caused a decl ine in the accuracy of the test. Therefore a 70-d test with cattle wei ghed every 2 wk seems to be optimal for measuring these traits in Brit ish breed cattle.