A crossbreeding experiment between four maternal lines of rabbits was carried out to estimate the crossbreeding effects on litter size components. The experiment was designed as a complete diallel crossing involving A, V, H and LP lines, all of these lines have been selected for litter size at weaning. A total of 2025 does, from the sixteen genetic types were subjected to laparoscopy. The sixteen genetic groups were distributed in four Spanish farms but only one group was presented in all farms to connect the data (line V). The recorded traits were ovulation rate (OR), number of implanted embryos (IE), total born (TB), number born alive (NBA), embryo survival (ES), fetal survival (FS) and prenatal survival (PS). An animal model was used to estimate components of variance using a REML procedure. Contrasts to show the differences between direct genetic effects of lines, differences between maternal genetic effects of lines and individual heterosis were estimated according to Dickerson model after solving the appropriate animal model conditioned on the REML variance components. In general, relevant but no always significant differences between lines in direct genetic effects were found. Line LP presented higher direct genetic effects than the other lines, significantly different from line A. All contrasts of maternal effects were not significant except between the LP and V lines. High positive values of heterosis contrasts were found between lines A and H. The cross between lines LP and V had negative heterosis for all traits with considerable negative effects on TB and NBA (16% and 11% of the mean, respectively). |
