Genetic relationship between growth traits in Bonsmara heifer and bull calves on different nutritional regimes

Author: H.E. Theron, M.M. Scholtz and C.Z. Roux
Year: 1994
Issue: 2
Volume: 24
Page: 67 - 70

A system of feeder–breeder dimorphism (large, fast growing offspring in feedlots obtained from small, low mainten¬ance cows on natural pastures) would be profitable in South Africa. The possibility of a genetic basis for feeder–breeder dimorphism was estimated by calculating genetic correlations between body mass gains achieved by beef cattle bulls in feedlots and body mass gains of half-sib heifers under natural pasture conditions (nutritional, managerial and sex differences between groups). The genetic correlations were 0.79 ± 0.11, 0.01 ± 0.19 and 0.43 ± 0.15, respectively for 12-month weight, ADG (average daily gain, weaning to 12 months) and the Kleiber ratio (ADG/ metabolic 12-month weight). The genetic correlations for ADG and the Kleiber ratio may indicate that different genes affect the measurements in half-sib bulls and heifers in different environments. The weaning to 12-month traits in bulls under feedlot conditions are probably genetically independent of the weaning to 18 months or 12 to 18 months traits in heifers under pasture conditions, as the genetic correlations for ADGs and Kleiber ratios of these traits are closer to zero than to unity (between –0.13 and +0.27). Selection for growth of bulls in feedlots would thus not affect the growth of heifers on pastures, which indicates that feeder–breeder dimorphism can be genetically induced for different nutritional environments.

Keywords: Bonsmara cattle, feeder–breeder dimorphism, genetic correlation, growth traits
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