Indian Journal of Animal Research

The present study was conducted on data of reproductive traits (viz., age at first service and age at first calving) in Jersey crossbred heifers, maintained at the Eastern Regional Station of ICAR-National Dairy Research Institute, Kalyani, West Bengal over a period of 38 years (1977–2014) to determine the effects of genetic and non-genetic factors. The data were classified according to season of birth, period of birth of animals and distributed in eight genetic groups having different level of Jersey inheritance. The least square mean of age at first service (AFS) and age at first calving (AFC) were 750.61±12.35 and 1089.36±13.99 days respectively. Sire had highly significant (P<0.01) influence on both AFS and AFC in the present study whereas, the genetic group had only significant effect on age at first calving. The half-bred of Jersey and Tharparkar crosses (1/2 Jersey-1/2 Tharparkar) had significantly lower AFC (987.47±43.21 days) than half-bred of Jersey and Red Sindhi and other crosses in this study. Moreover, the animals having less than 50% and more than 62.5% Jersey inheritance had highest AFC than other crosses. On the other hand, period of birth had significant effect on both AFS and AFC; however, season of birth only influenced AFC. Heritability estimates of AFS and AFC were observed 0.46±0.19 and 0.30±0.19 respectively. Strong genetic correlation (0.81±0.19) was estimated between these traits. Since, these traits have moderate to high heritability, it indicates faster improvement of these traits through selection