Estimation of crossbreeding parameters for fertility traits in dairy cattle

In the sixties breeding of the German Black Pied Dairy Cattle (SMR) has been initiated in East Germany by systematic crossing Holstein-Friesians and Jersey with the local Black Pied Cattle. First to fourth lactation records of about 820,000 (1st lactation), 650,000 (2nd lactation), 500,000 (3rd lactation) and 340,000 (4th lactation) purebred and crossbred cows, that had calved For the first time between the years 1970 and 1984, were included in the investigation. Traits under analysis were calving interval, days open and number of inseminations per service period. The large number of purebred (3) and crossbred (68) genetic groups made it possible to estimate epistatic effects. Models used were derived by DICKERSON (1969), KINGHORNS (1987), GROSSHANS et al. (1994) and WOLF et al. (1995). Holstein-Friesians showed significant positive additive-genetic effects on calving interval in the range from 8,67 to 16,21 days and similar effects for days open. Also the number of inseminations were significantly increased by the additive-genetic effect of Holstein-Friesians. For the additive-genetic effect of Jerseys a significant reduction of the calving interval in the first lactation could be found, whereas in the fourth lactation a significant prolongation of days open was evident. Heterosis effects in two-breed-combinations with Jerseys showed the tendency to reduce calving interval and days open, whereas the two-breed-combination Holstein-Friesian by Black Pied Cattle increased the calving interval. Epistatic effects influence all fertility traits analysed significantly. Two breed combinations with Holstein-Friesians showed recombination and additive x additive effects significantly reducing the calving interval in some lactations, but the days open in most lactations. Jersey by Black Pied Cattle crossbreds reduced calving interval in the first lactation through their recombination and additive x additive effects, but in the higher lactations the sign of these effects reversed. Other epistatic effects seemed not of higher importance.