The Council on Dairy Cattle Breeding (CDCB) announced several significant changes for the Dec. 2, 2014 U.S. dairy cattle genetic evaluations. First, two additional fertility traits will be incorporated into lifetime merit indexes. Rather than using daughter pregnancy rate (DPR), the indexes will include heifer conception rate (HCR) and cow conception rate (CCR). CDCB Chief Executive Officer João Dürr explains that incorporating the new fertility traits should be a more direct use of age at first calving and decreased costs to obtain pregnancies, including reduced semen needs. The revised net merit index places more relative emphasis on milk component traits, compared to previous evaluations. Combined fat and protein yield will now receive 42%, compared to the previous 35%. Less emphasis will be given to somatic cell score, body size and productive life.
A new index grazing merit (GM$) will be added to the December 2014 genetic evaluations. GM$ is geared toward herds on pasture systems, with those breeders often demanding higher fertility, compared to conventional systems, due to seasonal calving requirements. CDCB will continue to publish the traditional indexes net merit (NM$), cheese merit (CM$) and fluid merit (FM$).
In addition to the index updates, the December 2014 genetic evaluations incorporate a base change, which typically occurs about every five years. According to CDCB staff, the updated genetic base is simply an adjustment to the Predicted Transmitting Abilities (PTA) of all animals to compensate for the genetic change that has been made over the past five years and adjusting the base keeps PTAs from becoming extreme over time. Without the adjustment, users could lose sight that some genetics would not provide them the improvements they expect. Average PTAs in each breed for sire-identified cows born in 2010 will be set to zero, except for calving ease and stillbirth rate. Calving ease will be set at the breed average and somatic cell score will be set at 3.0.
Preliminary genomic predictions will now be calculated weekly, rather than just publishing official monthly evaluations. The weekly genomic predictions only include new genotyped animals and estimates of single nucleotide polymorphism (SNP) effects from the previous official evaluation. Also, reliabilities and genomic inbreeding will not be included in the preliminary genomic predictions. Earlier access to genomic evaluations benefits producers by enabling earlier culling decisions, and for genotyping laboratories, this fosters more uniform workloads.
More comprehensive descriptions of the merit indexes, preliminary genomic predictions and base change are available at https://www.cdcb.us/News/News.htm.
CDCB conducts genetic evaluations for economically important traits of dairy cattle. The CDCB allied partners cooperator database is the largest in the world, which is devoted to dairy animals, with more than 120 million female phenotypic records and more than 480,000 males receiving genetic evaluations or genomic predictions.