International evaluations for clinical mastitis in Brown Swiss

Abstract

The SNP training for clinical mastitis (STCM) trait was introduced by the Interbull Centre in April 2021. Previously, the mastitis trait within the udder trait group allowed for a wide range of trait definitions: direct clinical mastitis, somatic cell score, or a combination of clinical and subclinical mastitis. Since the introduction of STCM, the Council on Dairy Cattle Breeding (CDCB) has participated with data for Holsteins and Jerseys, aiming to enhance the domestic SNP reference population with foreign evaluations. As expected, for Holstein and Jersey the inclusion of Multiple Across Country Evaluation (MACE) evaluations had a minor impact on the US evaluation due to the dominance of US animals in the reference population. In the August 2022 evaluation, Brown Swiss (BSW) animals began receiving domestic health evaluations in the US, which were also incorporated into the Net Merit Index. During the January 2023 test run, the BSW STCM successfully completed Trend Methods I and III validation at Interbull. Effective as of the April 2023 evaluation and going forward, BSW foreign evaluations are included in the United States of America (US) clinical mastitis evaluations. The initial expectation was that the impact of this inclusion would be limited, as only two other foreign countries (France and Switzerland) contribute to the Interbull clinical mastitis evaluation. However, the observed impact on the evaluations was noticeable. Correlations between April 2023 and March 2023, triannual genomic evaluations were as low as 0.73 for reference animals and 0.56 for young animals. Along with the significant variation in Genomic Estimated Breeding Values (GEBV), the mean genomic reliabilities (GREL) for young animals increased from 24% in March 2023 to 30% in April 2023. These results can be explained by two main factors: i) the contribution of foreign bulls from France and Switzerland in the SNP reference population for US BSW made the inclusion of MACE evaluations more relevant; ii) a large number of US BSW clinical mastitis records became available prior to the April 2023 evaluation and were added to the national cooperator database. Large changes in GEBV and GREL resulting from the initial inclusion of foreign data are not expected in subsequent evaluations unless more countries participate.