Abstract
Data from the Red Sindhi-Jersey crossbreeding investigations conducted at three stations were studied to determine the possible effects of varying degrees of Sindhi inheritance on gestation length, birth weight and age at first calving. Each 25% of Sindhi inheritance increased gestation length approximately three days, thus suggesting an additive genetic effect. Parity of calving, sires within breeds and interaction of sire and sex had a significant effect on gestation length but sex differences were not significant. Gestation length, age of dam, sires within breeds and the interaction of sex and sire had significant effects on birth weight. The interaction of sex and breed was not significant. The F1 crossbred calves showed heterosis for birth weight even after adjustment for gestation length. The ¾ J calves were heavier at birth than Jerseys but this might be attributed primarily to increased gestation length. The ¼ J crossbred calves were generally smaller than any of the other groups and the differences were more pronounced when gestation length was considered. The results of this study indicate that up to 75% Sindhi inheritance may be used in combination with Jerseys without delaying the age of first calving beyond that normally considered satisfactory for purebred Jerseys. Copyright © . .