Evaluation of testing schemes with clones for carcass traits in beef cattle
2000
Hirooka, H. (Ryukoku Univ., Kyoto (Japan))
The annual genetic responses per genetic standard deviation (genetic gains) for carcass traits in beef cattle were compared for clone testing schemes and combined testing schemes of clone testing schemes and progeny testing schemes, and the optimum sizes of the clone group (the number of members in a clone) for these schemes were investigated. In the clone testing scheme, a bull in clone members is left as a candidate and the remainders are slaughtered and their carcass traits are taken measurements. In the combined testing scheme, the candidate bulls are progeny tested after clone testing to improve selection accuracy and they are selected by the selection index based on information from measured clone members and progeny. All comparisons in this study were done under the constraint of the constant testing ratio, K, the ratio of the number of tested animals to the number of selected candidate bulls. In the clone scheme, the genetic gain and the optimum size of clone groups increased with increasing K. In the combined testing scheme, increasing K resulted in increased optimum group sizes of clones, and the genetic gain decreased with increasing the size of progeny groups. When non-additive genetic effects were assumed to be present, genetic gains were low and the optimum sizes of clone groups were small. In all cases, the higher genetic gains were obtained in clone testing schemes than in the conventional progeny testing scheme in Japan
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