Breeding work in dairy cattle is important for improving the productivity and profitability of the dairy sector. Traditionally, the main goal of breeding dairy cattle was to improve milk yield, but other desirable traits such as health and fertility have now globally become important breeding objectives. Recent research has also sought to include traits related to sustainability and climate impact.
Mating the right cow with the right bull
In 2008, a new breeding technique called genomic selection became available for use in dairy cattle breeding. It applies information from the DNA of cows to predict how good they are in terms of different traits, such as milk yield, health, fertility and sustainability. In the early days, DNA testing was expensive and was only used for candidate bulls for artificial insemination. Today, the cost has decreased so that is possible to test whole herds. In addition to producing the best animals, you can also avoid unnecessary inbreeding and avoid genetic defects.
In his doctoral thesis, Christian how genomic information can be used at herd level, mainly considering better mating plans. Or simply: how we inseminate the right cow with the right bull using DNA information.
– We compared genomic breeding values and parent average breeding values for young females in terms of their ability to predict cow performance later in life. The aim was to increase confidence in genomic breeding values among farmers. We showed that genomic breeding values predicted future traits significantly better, says Christian.
Less inbreeding while preserving the positive characteristics
In another study, Christian optimsed matings for Red Dairy Cattle at herd level based on economic score for different mating options within each herd, considering genetic level, relatedness, and probability of genetic defects being expressed.
– It was possible to reduce genetic relatedness between parents with minimal effect on genetic level. It was never economically advantageous to inseminate a female carrying a recessive genetic defect with a bull carrying the same genetic defect. A longer calving interval and an extra insemination cost more than what an optimal mating for other factors can compensate for, says Christian.
Mating plans for Holstein
Later, the Holstein dairy breed was also studied, the study also included positive characteristics of the cows, for example polledness. The results were consistent with the study of Red Dairy Cattle in terms of genetic relationships and defects. In addition, it was possible to increase the frequency of cows without horns without negatively impacting other criteria.
Long-term mating planning
But what is the long-term impact of genomic mating allocations? In another study in the thesis, Christian showed that compared with only maximising genetic level, including any genetic relationship in the economic score lowered the rate of increase in inbreeding, with minimal effect on genetic gain. In addition, the risk of known genetic defects being expressed was reduced and positive characteristics could be increased. Using more bulls, which helped lower the rate of inbreeding, was favourable regarding the number of animals that were carriers of genetic defects, which reduced the risk of expression in future generations.
– Going forward, we need more research on the different ways of calculating genomic relatedness and how well they are at predicting inbreeding and its effects. This is especially important for the Jersey breed and for Nordic Red Dairy Cattle, for which research is limited to the Nordic countries, concludes Christian.
Christian will defend his thesis in February
Christian’s defence for the degree of Doctor of Philosophy will take place in Sal L, SLU, Ultuna, February 7, 2024, at 09:15. The external reviewer is Professor Donagh Berry from Animal & Grassland Research and Innovation Centre in Ireland. For more information about Christian’s defence contact him at the e-mail below.
