Search

In this study, we explored mating allocation in Hol-stein using genomic information for 24,333 Holstein fe-males born in Denmark, Finland, and Sweden. We used 2 data sets of bulls: the top 50 genotyped bulls and the top 25 polled genotyped bulls on the Nordic total merit scale. We used linear programming to optimize economic scores within each herd, considering genetic level, genetic relationship, semen cost, the economic impact of genetic defects, polledness, and 0-casein. We found that it was possible to reduce genetic relation-ships and eliminate expression of genetic defects with minimal effect on the genetic level in total merit index. Compared with maximizing only Nordic total merit in-dex, the relative frequency of polled offspring increased from 13.5 to 22.5%, and that of offspring homozygous for 0-casein (A2A2) from 66.7 to 75.0% in one genera-tion, without any substantial negative impact on other comparison criteria. Using only semen from polled bulls, which might become necessary if dehorning is banned, considerably reduced the genetic level. We also found that animals carrying the polled allele were less likely to be homozygous for 0-casein (A2A2) and more likely to be carriers of the genetic defect HH1. Hence, adding economic value to a monogenic trait in the economic score used for mating allocation sometimes negatively affected another monogenetic trait. We rec-ommend that the comparison criteria used in this study be monitored in a modern genomic mating program.

The aim of this study was to predict genomic breeding values for metabolic body weight (MBW) by a single-step model and to compare obtained breeding values to those from a multistep genomic prediction model and a pedigree-based BLUP model. Data contained over 3 million observations from Danish, Finnish and Swedish Red dairy cattle born in the years 1990 to 2017. The applied multiple-trait animal models included six traits: 1st, 2nd, and 3rd parity MBW, and first parity stature, chest width and body depth. Breeding values from the singlestep model were in good agreement with those from the multi-step model (correlations were 0.98-0.99), but BLUP breeding values differed from genomic breeding values slightly for bulls and clearly for cows. The single-step model gave higher validation reliabilities for bulls and cows than the multi-step model. The results support using a single-step approach for the genomic evaluation of MBW.

The development of breeding tools, such as genomic selection and sexed semen, has progressed rapidly in dairy cattle breeding during the past decades. In combination with beef semen, these tools are adopted increasingly at herd level. Dairy crossbreeding is emerging, but the economic and genetic consequences of combining it with the other breeding tools are relatively unknown. We investigated 5 different sexed semen schemes where 0, 50, and 90% of the heifers; 50% of the heifers + 25% of the first-parity cows; and 90% of the heifers + 45% of the first-parity cows were bred to sexed semen. The 5 schemes were combined in scenarios managing pure-breeding or terminal crossbreeding, including genomic testing of all newborn heifers or no testing, and keeping Swedish Red or Swedish Holstein as an initial breed. Thus, 40 scenarios were simulated, combining 2 stochastic simulation models: SimHerd Crossbred (operational returns) and ADAM (genetic returns). The sum of operational and genetic returns equaled the total economic return. Beef semen was used in all scenarios to limit the surplus of replacement heifers. Terminal crossbreeding implied having a nucleus of purebred females, where some were inseminated with semen of the opposite breed. The F-1 crossbred females were inseminated with beef semen. The reproductive performance played a role in improving the benefit of any of the tools. The most considerable total economic returns were achieved when all 4 breeding tools were combined. For Swedish Holstein, the highest total economic return compared with a pure-breeding scenario, without sexed semen and genomic test, was achieved when 90% sexed semen was used in heifers and 45% sexed semen was used for first-parity cows combined with genomic test and crossbreeding (+(sic)58, 33% crossbreds in the herd). The highest total economic return for Swedish Red compared with a pure-breeding scenario, without sexed semen and genomic test, was achieved when 90% sexed semen was used in heifers combined with genomic test and crossbreeding (+(sic)94, 46% crossbreds in the herd). Terminal crossbreeding resulted in lower genetic returns across the herd compared with the corresponding pure-breeding scenarios but was compensated by a higher operational return.