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Accounting for numbers of expressions of specific genotypes using a modified gene-flow method

Nishio, M., Kahi, A.K., Hirooka, H.
Livestock science 2008 v.114 no.2-3 pp. 241-250
beef cattle, Wagyu, gene expression, genotype, gene flow, bulls, alleles, animal breeding, gene frequency, simulation models, recessive genes, loci, quantitative traits, marbling, mortality, economic analysis, breeding value
The objective of this study was to develop a modified discounted gene-flow method and calculate numbers of cumulative discounted expressions (CDE) and value of using a Japanese Black cattle bull carrying specific alleles of interest. The discounted gene-flow method was modified to consider not only parent's genotypes but also the allele frequency in the herd. Input parameters representing a typical situation in a Japanese Black cattle herd were used to calculate the CDE and the value of using sires genotyped for recessive genes assuming biallelic loci (A and a) and a herd at Hardy-Weinberg equilibrium. The quantitative trait assumed was marbling and the effect of genotype aa was 1 Beef Marbling Standards (BMS) above that of an animal with either genotype Aa or AA. The effects of gene frequency and discount and survival rates on the CDE were determined for different genotypes of sires. Benefits from using either aa sires or Aa sires above that of using unknown sires at various gene frequencies were also determined. The CDE of aa sires were larger than those of Aa sires under all gene frequencies. The differences in the CDE between aa and Aa sires ranged from 34% at gene frequency of 0.7 to 71% at gene frequency of 0.01. An increase in the discount rates and a decrease in survival rates were associated with a decrease in expressions in cases using aa and Aa sires. The benefits of using aa sires were high when the gene frequency in the herd was 0.5. The benefit of aa sires were approximately 3023 yen more than that for unknown sires in the population when the gene frequency was 0.5. At gene frequencies higher than 0.5, use of Aa sires was not beneficial. This study has demonstrated how the gene frequencies in the herd and the genotypes of sires are critical in determining the benefits of using single recessive gene in the Japanese Black cattle.