Genetic Correlation Analysis of Calving Ease and Gestation Length of Korean Holstein Cattle.

Objective: To investigate genetic correlation between calving ease (CE) and gestation length (GL) traits of Korean Holstein cattle to understand genetic structures of these two traits and their potential implications.

Methods: Records of progenies from first parity (P1, N=117,921) and second parity (P2, N=141,104) Holsteins cows were used for analysis. All phenotypes (CE and GL) were considered as calf traits. The CE was an ordered categorical trait. It was scored from 1 (normal calving) to 4 (difficult calving). GL observations were restricted between 260 and 305 days. Variance components and genetic parameters were estimated through a bivariate animal model with a correlated maternal effect using the BLUPF90+ software package.

Results: Heritability (h2) estimates of CE for direct and maternal effects were low (less than 0.01) in all parity calves. For GL, despite lower h2 of maternal effect (~0.03), the direct effect was moderately heritable (0.20 to 0.23) in this study. Direct and maternal effects of CE trait were weakly correlated (P1: 0.09 ± 16.60, P2: -0.04 ± 0.00). GL had similar correlation patterns (P1: 0.03 ± 0.00; P2: -0.15 ± 0.05) across parities. Direct genetic correlations of GL and CE were mostly weak (P1: 0.18 ± 0.31; P2: -0.01 ± 0.06), whereas maternal genetic correlations were moderate and positive (P1: 0.39 ± 0.95; P2: 0.46 ± 0.04). Although the genetic influence of GL on CE was not entirely clear due to large estimation errors for parameters, overall positive associations between direct effects and maternal effects essentially indicate a selection potential for GL as an indicator trait of CE.

Conclusion: This is the first genetic correlation investigation of GL and CE in Korean Holstein cattle. It provides important insights into genetic architectures of GL and its future potential as an indicator trait for CE improvements in Korean Holsteins.