Calving Traits to Reflect Breed Averages
With the August 11, 2020 sire summary, noticeable changes will be seen in the calving traits as reported by the Council on Dairy Cattle Breeding (CDCB). What brought about these changes? It comes down to a combination of a model update (which occurred in April 2020) as well as updating these traits to reflect incident rates seen on farm.
April 2020 Sire Summary
〉 The calving trait model was updated to exclude herds that report all easy calvings and to adjust the categories producers use to record calving difficulty.
Post April 2020
〉 After the model change, a mismatch was identified between PTA calving traits and the actual rate of dystocia (difficult births) and stillbirths on farm.
August 2020 Sire Summary
〉 Calving traits will be adjusted to reflect incident rates seen on farm.
〉 Because progress has been made, calving traits will see MUCH lower PTAs.
History of Calving Traits
Historically, the breed average phenotypic base for Holsteins was set at 8.0%. Calving difficulty on farm has been aggressively selected for and, as a result, steadily decreased over time. With the April 2020 model updates, it became evident the calving traits did not match real-world incident rates. The genetic base was updated but not the phenotypic base – which has been kept constant for several years as a result of an industry-wide focus on reducing calving difficulty.
New Phenotypic Base
With the August 2020 sire summary, CDCB will adjust the phenotypic base to match the observed incident rates. This adjustment will cause a noticeable decrease in average PTA for calving ease and stillbirths (Table below).
〉 The phenotypic base will be adjusted to match observed incident rates in calving traits. Holstein PTAs will average 2.2% for Sire Calving Ease (SCE) and 2.7% for Daughter Calving Ease (DCE).
〉 The range of SCE will decrease (with the majority of bulls ranging from 1% to 4%).
〉 The PTA reliabilities will remain the same, as a change in the phenotypic base does not affect the amount of information contributing to the PTAs.
〉 There are more subtle changes in stillbirth evaluations, updated to reflect only births to heifers vs. all animals.
Minor Adjustments Made to ICC$™ Index
With the August sire summary, minor changes are being made to the GENEX ICC$™ indexes for Holsteins and Jerseys to make them even better selection tools for today’s modern dairy producers.
Building on ICC$’s animal health emphasis, the Mastitis trait recently released by the Council on Dairy Cattle Breeding (CDCB) is being incorporated into both the Holstein and Jersey ICC$™ indexes. It will replace the previously used Mastitis Resistance trait published by the Canadian Dairy Network (CDN). The CDCB Mastitis trait has a larger dataset which improves the reliability (see below). This change does not impact trait weightings within the formula; it is simply a change in data source.
Within ICC$™ for Jerseys the GENEX proprietary trait Age At First Calving (AAFC) is also being replaced by the CDCB Early First Calving (EFC) trait. When AAFC trait was established three years, there were no other similar industrywide evaluations. Today, EFC is available and offers about a 5% increase in reliability. Again, there was no change in trait weighting within the index formula.
Within ICC$™ for Holsteins, the HH6 haplotype is being added to the Fertility Haplotypes section of the Fertility & Fitness (FERT$) sub-index. Also, the standard deviations are being lowered for the four calving traits within the Calving Ability (CABL$) sub-index.