책임운영기관 농촌진흥청 국립축산과학원

The number of Jersey cattle raised in the Korean dairy industry has been steadily increasing; however, their population size remains small compared with Holsteins, and studies on their genetic characteristics are still limited. This study aimed to establish a genetic reference for the Jersey population in Korea by characterizing the genetic structure of domestic Jersey and Holstein populations and quantitatively evaluating changes in breed composition across successive backcross generations (F1 to F6) produced by mating Jerseys to Holsteins. Using the Illumina BovineSNP50 V3 SNP chip, a total of 53,218 SNPs were genotyped, and after quality control, 26,931 SNPs shared among 494 Jersey, 742 Holstein, and 98 crossbred animals were retained for downstream analyses. Principal component analysis (PCA) clearly separated Holstein and Jersey cattle into two distinct genetic clusters, demonstrating substantial genetic differentiation between the breeds. Supervised ADMIXTURE analysis revealed a progressive increase in Jersey ancestry across backcross generations, with mean Jersey proportions of 0.55 in F1, 0.74 in F2, 0.87 in F3, and 0.99 in F4. Notably, animals from the F4 and later generations clustered almost entirely within the Jersey group in the PCA plot, indicating convergence toward a genetic composition effectively indistinguishable from purebred Jerseys.These patterns were consistent with theoretical expectations of backcrossing (F1: 50%, F2: 75%, F3: 87.5%, F4: 93.75%) as well as international criteria for breed purity recognition (e.g., the 7/8 standard of the Canadian Animal Pedigree Act and the U.S. Council on Dairy Cattle Breeding (CDCB) purity threshold of Breed Base Representation (BBR) ≥ 94%). Overall, this study provides a foundational reference population for Jerseys in Korea and establishes an analytical framework for accurately determining breed composition in crossbred cattle. The findings offer essential resources for setting registration criteria for backcross progeny, improving pedigree management, supporting breeding program decisions, and guiding national strategies for genetic resource conservation in the Korean dairy industry.