Faculty of Technical Sciences

In contrast to other species, production animals in dairy cattle are mainly purebreds. However, crossbred cows are becoming more widespread due to better profitability from heterosis of economically important production and health traits. Currently, breeding goals (BGs) for purebreds used in crossbreeding systems are optimized for maximizing genetic gain in purebred cows. This might not be optimal when the aim is to increase heterosis and breed complementarity in order to maximize profit in crossbred cows. We hypothesize that differentiated BGs in purebreds that complement each other can improve the performance of crossbred production animals. To test this hypothesis, we set up a pure- and crossbreeding design using the simulation tool ADAM with two breeds, Danish Jersey (DJ) and Nordic Holstein (NH). Real marker genotypes from these two breeds were used as reference to resemble the real population structure of the two breeds. A progeny testing scheme was simulated for 20 years to build large genomic reference populations in each breed followed by a genomic testing scheme of 5 years. Finally, one generation of crossbreeding between the two purebreds was generated. The BG in the purebreds included two traits, a production trait and a health trait, with a genetic correlation between the 2 traits of -0.46 for DJ and -0.35 for NH. Three BGs with different economic values of the traits were set up to test the hypothesis: (1) a reference scenario resembling the
weights in the present Nordic total merit index for DJ and NH; (2) the same BG in NH as in 1 but in DJ the BG had a higher weight on health; and (3) BGs only weighing production in NH and health in DJ. The three scenarios was evaluated in the crossbred population according to genetic level and dominance. Preliminary results show a higher degree of dominance in the crossbred animals compared to the purebred animals, but a lower genetic level, especially in scenario 3. The outcomes of this study can be used to evaluate the value of setting up BGs in purebreds specified for crossbreeding