The most significant change for the April 2, 2024, triannual evaluations is an adjustment in the trait model for six CDCB health evaluations – Resistance to Milk Fever (MFEV), Displaced Abomasum (DA), Ketosis (KETO), Mastitis (MAST), Metritis (METR) and Retained Placenta (RETP).
Since these traits debuted six years ago, the number of health records in the National Cooperator Database has tripled or quadrupled – depending on the trait. Detail here. With this data surge, the trait model has been adjusted with new variance component estimates and adjusted weights, effective with April 2024 evaluations. This evolution follows the typical progression of newer traits.
These CDCB evaluations for disease resistance were first launched for Holstein in April 2018, Jersey in April 2020, and Brown Swiss in August 2022. Variance components were originally estimated in 2018, when Holstein records available ranged from 1.2 to 2.2 million per trait. Current volume ranges from 4.3 to 7.7 million for the three breeds, with Mastitis having the most records in CDCB’s database.
In a test run comparing the previous and updated model, correlations of genomic estimated breeding values (GEBV) for five of the traits were ≥0.96 for Holstein, ≥0.90 for Jersey and ≥0.92 for Brown Swiss. For Displaced Abomasum, lower correlations were observed (≥0.95 HO, ≥0.82 JE and ≥0.81 BS) due to the largest change in heritability.
With the model adjustment, variation in Predicted Transmitting Ability (PTA) for some individual animals, particularly Jersey and Brown Swiss, can be expected. The impact on Net Merit is expected to be very small, given the weighting of these traits in the index.
Read detail on health records, model effects, new variance component estimates, adjusted weights and correlations between old and new model in the triannual change document by CDCB and USDA AGIL.