This study was conducted to use the pedigree information of Hanwoo cows participating in the Hanwoo cow test project to examine changes in pedigree completion, inbreeding coefficient, and effective group size. As of 2020, 273,381 cows participating in the Hanwoo cow test project were used, and the final 581,816 data were used for analysis by inquiring up to 13 generations of pedigree records. The pedigree completeness index(PCI) analysis used only individuals who knew both parents and whose parents knew at least one parent. According to the analysis, pedigree completeness and average coefficients are increasing gradually with the year of birth, with the mean coefficient of the lastest animals with accumulated pedigree records relatively low. The results of estimating the effective group size were estimated in the range from 215 animals(1999-2019) to 51 animals(2018-2019), indicating a trend in which the effective group of groups containing animals born in the past rapidly decreases over time. Through the Hanwoo cow test project, Hanwoo farmers should make continuous efforts to prevent inbreeding coefficient damage by customized breeding considering individual pedigree information and genetic ability, and to minimize the loss of genetic diversity by mitigating the concentration of bulls. However, as many studies have shown, the effective group size is decreasing, and in order to maintain genetic diversity in Hanwoo groups, additional studies such as cow genomic selection, which can increase effective group size due to the variety of selection and breeding methods.
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