EFFECTS OF A ROTATIONAL CROSSBREEDING WITH 2 COMPLEMENTARY PIG BREEDS ON FERTILITY TRAITS .2. ESTIMATION OF CROSSBREEDING PARAMETERS

In a long term rotational crossbreeding between German Landrace (GL) and Pietrain (GP) breeds crossbreeding parameters were estimated for reproduction traits. The performance of 343 pigs of six different breeding groups were analysed. The analysis was based on Dickerson's models in two steps. The crossbreeding parameters were estimated after the estimation of the breeding group means and the variance-covariance matrix. The results may be summarised as follows: 1. The population difference between GL and GP with respect to fertility is due to the negative and significant or even highly significant individual additive genetic effects. 2. The ovulation rate is mainly determined by the additive genetic effects while the nonadditive effects play an important role for embryonal traits and litter performance. 3. Due to positive litter environment of crossbred sows, positive and mostly significant or highly significant individual and maternal heterosis of sows occur in fertility traits, which are generally understood as maternal and grandmaternal heterosis effects. 4. The heterosis effects in the first litter are larger than in the second litter because of heterosis x environment interactions.