Handling of inbreeding and semen sire breed in the Nordic Holstein fertility evaluations as part of EuroGenomics Harmonization standard.

Female fertility is a complex trait expected to be highly influenced by inbreeding level. Conception rate (CR), as part of the fertility trait complex, is known to be affected by the mating sire breed. EuroGenomics has decided to establish golden standards for genetic evaluation for all trait groups. Golden standards consider inbreeding in the genetic relationship (A) matrix, and inbreeding depression (effect of the past inbreeding). In fertility golden standard evaluations semen sire should be considered. Implications were tested using Nordic (Denmark, Finland, and Sweden) Holstein (HOL) multi-trait multi-lactation fertility evaluation models. Inclusion of the inbreeding into the A matrix had no significant effect on the fertility index but would be beneficial for future single-step implementation. The inbreeding depression was found to have limited effect in the HOL Nordic population. Effect of service sire breed was considered as important due to the increased use of beef semen in inseminations of dairy cows on second or later parities.