The Estimation of Genetic Parameters for Longevity According to Lactation Period Using a Multiple Trait Animal Model in Korean Holstein Cows

Simple Summary South Korea dairy farmers are less interested in improving milk production-related traits for various reasons, including the milk production quota system. Consequently, they have become more interested in improving traits associated with longevity. Therefore, the purpose of this study was to analyze the culling patterns and survival rates of Korean Holstein cows and evaluate genetic characteristics related to parity and longevity of each lactation by using test data collected in South Korea. This study presents evidence that individuals' genetic backgrounds differ with respect to differences in the individuals' survival periods. Three lactation periods in each parity were split according to lactation days: 0-90 days (1), 91-299 days (2), and 300 days to the next calving (3). The heritability of the first, second, and third parities were 0.020, 0.028, and 0.039, respectively. In all parities, the heritability in late-lactation was higher than that in early- and mid-lactations. Most genetic correlations for survival in the first parity were higher than those in the second and third parities. The genetic correlation in the same lactation in the first and second parities were lower than those in the intervals in the second and third parities. The results of this study may serve as a basis for developing a more accurate model for evaluating longevity traits in South Korea. Longevity is closely related to the survival rate of dairy cattle and refers to the period during which the cow has economic value, from first calving to culling. The purpose of this study was to analyze the culling patterns and survival rates of Korean Holstein cows and evaluate genetic characteristics related to parity and longevity of each lactation by using the test day milk yield collected in South Korea. The performance data of the dairy cattle were collected from 2004 to 2019 by the Nonghyup Dairy Cattle Improvement Center. The collected 1,702,304 records were used as pedigree data through the Korea Animal Improvement Association. The lactation period was divided into early-lactation (0-90 days: L1.1, L2.1, and L3.1), mid-lactation (91-299 days: L1.2, L2.2, and L3.2), and late-lactation (300 days-next parity: L1.3, L2.3, and L3.3). The heritability of longevity for the first, second, and third parity was 0.020, 0.028, and 0.039, respectively. In all parities, the heritability in late-lactation was higher than that in early- and mid-lactation. Most genetic correlations for survival in the first parity were higher than those in the second and third parities. The results of this study may serve as a basis for developing a more accurate model for evaluating longevity traits in South Korea.