Relationship between Fertility and Milk Production Traits in Pure Jersey Dairy Cows: Multitrait Analysis

Records on 22175 pure Jersey dairy cows evaluated the genetic and phenotypic correlations. Data for this study were collected from Adea Berga dairy research farm span over 33 years (1986-2019) performance records. Five fertility; number of services per conception (NSC), days open (DO), calving interval (CI), age at first calving (AFC), age at first service (AFS), and three-milk production traits; lactation milk yield (LMY), daily milk yield (DMY), lactation length (LL) were estimated by WOMBAT software fitted a multitrait repeatability animal model. The result of present study revealed that genetic correlations among fertility traits for pure Jersey cows varied from -0.63 to 0.91 whereas the values of phenotypic correlations were found to be ranged from -0.28 to 0.98. The AFS-AFC was the highest genetic and phenotypic correlations among all fertility traits. The lowest genetic and phenotypic correlations were between AFS/AFC-CI and AFS/AFC-NSC, respectively. For milk production traits, the genetic correlations ranged from 0.86 to 0.96 whereas the values of phenotypic correlations were found in the range of -0.05 to 0.82. The LMY-LL was the highest genetic and phenotypic correlation and DMY-LL was the lowest. The genetic correlations between reproductive and milk production traits also varied from -0.38 to 0.42 and phenotypic correlations ranged from 0.13 to 0.48. The highest genetic and phenotypic correlations for reproductive and milk production traits were from DO-LL and LMY-CI/DO whereas the lowest was from NSC-LL and AFS-LL, respectively. Genetic correlations among the traits in the present study were higher than the corresponding phenotypic correlations among all milk production traits and the majority of fertility traits. The positive genetic correlations among traits in the present study would broaden the choice selection of more traits at one time for improvement. To improve genetic progress and breeding efficiency of Jersey dairy cows, periodic evaluation of the genetic and phenotypic relationship of dairy traits should be applied and more than one trait should be selected based on the magnitude of correlations (more correlated traits).