Analysis on crossbreeding in the Dutch dairy cattle population
This study aimed to estimate heterosis for 305d-milk, fat and protein, and for calving interval in the Dutch dairy cattle population. Six breeds and 11 types of crosses were considered. A total of 5.913.654 and 3.679.183 primiparous cows were used for productive traits and for calving interval, respectively. Pedigree file was used to carry out the evolution by birth year (from 1976 to 2003) of the gene frequency in the Holstein Friesian (HF), Dutch Friesian (DF), and Mosa-Reno-Yssel (MRY) Dutch population. The effects included in the model of analysis, performed using software PEST, were: herd, year-season of calving, age at calving, lactation length, cross and random animal genetic effect. In the model for calving interval lactation length effect was replaced by 305d-milk yield. Means of 305d-milk, fat, and protein were high for HF and equal to 7300 kg, 315 kg, and 250 kg, respectively. Concerning calving interval, the best value was found for MRY (387 days). Non-additive genetic estimates for productive traits ranged from 0.8% (305d-fat) to 10.2% (305d-protein). Heterosis for calving interval appeared higher in crosses involving Brown Swiss (BS) and Montbéliarde (M) breeds, with values between -4.9% and -3.0%, corresponding to -12 and -21 days of calving interval, respectively. In conclusion, for yield traits higher percentages were provided by crosses in which Jersey (J) was present, while for calving interval combinations with BS performed better than others concerning heterosis. Future perspectives could consider the F1 following crossbred cows in order to estimate recombination losses.