Genetic evaluation of bulls with economic weights equivalent to relative desired gains in Japanese Shorthorn

摘要

Japanese Shorthorn bulls have been selected based on a selection index after performance test, and based on independent culling levels after progeny test. A scheme was proposed for genetic evaluation of bulls using economic weights equivalent to desired gains of the traits measured in performance and progeny tests. The genetic parameters of six traits measured in performance and progeny tests were estimated. Using the parameters, the breeding values of the six traits on each bull were evaluated. Two breeding goals, A and B, were assigned. The breeding goal A was to restore 1.0 of beef marbling standard (BMS number) keeping daily gain in progeny test constant. The breeding goal B was to restore 1.0 of BMS number without any restriction on the othertraits. Two sets of weighting factors for the selection indices were calculated to realize the relative desired gains of the six traits for reaching the breeding goals A and B. The indices consisted of phenotypic values of the six traits. Using the twosets of weighting factors, two sets of relative desired gains to reach the goal A and B were transformed into two sets of relative economic weights for the six traits. The selections with Smith and Hazel type selection indices based on the economic weights are expected to bring us approximately equivalent relative genetic gains of the six traits to the relative desired gains to reach the breeding goals A and B. The economic weights make it possible to estimate the aggregate genotype of each bull. The sequential selections based on an aggregate genotype of bulls will result in consistent genetic improvement targeting a same breeding goal. All the testing stations of Japanese Shorthorn have been adopted the aggregate genotype for goal A as selection criterion in 1999. The future subject on the data collection in field was discussed.