Studies on Performance Testing for Growth Rate of Dual Purpose Bulls

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Abstract
Genetic parameters of daily gain and related traits were estimated in the performance testing of dual-purpose bulls in Sweden. The optimum size of contemporary groups was also investigated in order to elucidate the efficiency of the Contemporary Comparison method so far used in Sweden. Heritability for daily gain on test averaged 0.4, though the estimates varied between breeds, test stations and time periods. Genetic and phenotypic correlations between daily gain in different age intervals, and live weight at different ages were high in most cases, and higher the more closely spaced in time the traits were measured. The currently used contemporary groups could not properly adjust for seasonal influence on daily gain and simultaneously express the average genetic level of the population. To accomplish this it would be necessary to have a testing capacity of 140–200 bulls annually. This would make it possible to establish contemporary groups of 80–100 bulls within a time period of 6–7 months, which would be the maximum length of period to get a proper adjustment for seasonal variation in daily gain.