Revised genomic edits for heifer conception rate

By Paul VanRaden

Three changes were introduced in June to improve genomic predictions for heifer conception rate (HCR) in breeds with small reference populations such as Guernseys. 1) Multi-trait across country evaluations (MACE) of bulls are used in the HCR reference only if their reliability is at least 15% greater than reliability of parent average. This same edit had already been applied to MACE for cow conception rate (CCR). 2) A new edit for HCR does not use domestic bulls born before 1985 with HCR reliability less than 50% in the reference because this is not direct HCR information, only correlated information from CCR. 3) The deregression option for Guernseys and Ayrshires no longer removes data from genotyped progeny from their parents' evaluations to avoid double-counting. Very low HCR reliability made HCR evaluations in those breeds sensitive to this option. Correlations of HCR predictions for young animals before and after these edits were 0.05 for Guernseys, 0.96 for Brown Swiss, and greater than 0.99 for Ayrshires, Jerseys, and Holsteins. Some large changes occurred within the smaller breeds for foreign or very old bulls due to the lack of HCR data before 2000.