Reproductive Performance of Crossline and Pureline Dairy Heifers

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Abstract
Data of 2779 purebred and crossbred heifers collected from 5 research stations of Agriculture Canada were used to study additive and nonadditive genetic effects on ages at 1st heat and at 1st breeding and conception rate at 1st service. Of these heifers, 2378 heifers had information on ages at 1st conception and at 1st freshening, days from 1st service to conception and gestation length. The model included station, year of birth, sire, breed additive, maternal and heterosis effects where sire effects were treated as random. Station differences were a significant source of variation for all reproductive traits. Year of birth had significant effects on 4 of 7 reproductive traits. Breed additive effects for all genetic groups were not significant except for Finnish Ayrshire and American Holstein. No significant maternal effects were detected. Of 21 combinations of heterosis effects, 6 combinations showed significance. Partial regression coefficients ranged from negative to positive, suggesting that breed additive, maternal and heterosis effects could increase or decrease for each percent increase of genetic contribution, depending upon the trait, breed group and type of inheritance.