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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Animal Genomics and Improvement Laboratory » Research » Publications at this Location » Publication #412582

Research Project: Increasing Accuracy of Genomic Prediction, Developing Algorithms, Selecting Markers, and Evaluating New Traits to Improve Dairy Cattle

Location: Animal Genomics and Improvement Laboratory

Title: Six direct health traits for US: updated variance component estimates and implementation of variance adjusted weights

item MCWHORTER, TAYLOR - Council On Dairy Cattle Breeding
item PARKER GADDIS, KRISTEN - Council On Dairy Cattle Breeding
item NICOLAZZI, EZEQUIEL - Council On Dairy Cattle Breeding
item Vanraden, Paul

Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 3/10/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Six direct health evaluations for the resistance to milk fever (MFEV), displaced abomasum (DA), ketosis (KETO), mastitis (MAST), metritis (METR), and retained placenta (RETP) are provided to US dairy producers by the Council on Dairy Cattle Breeding (Bowie, MD). The evaluations were first incorporated into Merit Selection Indices as health dollars (HTH$) for Holstein in April 2018, Jersey in April 2020, and Brown Swiss in August 2022. The relative emphasis is 1.2% for Lifetime Net Merit, Fluid Merit, and Cheese Merit and 1.4% for Lifetime Grazing Merit. Phenotypes have more than doubled since variance components were last estimated in 2018, currently including 5.8m (1.06%) MFEV, 5.8m (1.63%) DA, 4.3m (5.84%) KETO, 7.7m (11.72%) MAST, 6.3m (7.16%) METR, and 7.6m (3.39%) RETP records (incidence rate). Health evaluations use a single-trait linear animal repeatability model. Variance components were estimated for random effects (additive, permanent environment, herd-by-year, and herd-by-sire) resulting in new overall heritabilities (h^2), h^2-by-lactation, and repeatability. Except for MFEV which maintained a 0.6% h^2, the h^2 increased from 1.1 to 3.1% for DA, 1.2 to 1.7% for KETO, 3.1 to 3.2% for MAST, 1.4 to 1.6% for METR, and 1.0 to 1.3% for RETP. To adjust for heterogeneous variance, in addition to the existing variance-adjusted phenotypes, weights were updated from 0 or 1 to a value estimated from the variance components. Both variance adjustments are used to standardize genetic variance across differing parities that have differing heritabilities. Correlations between the official December 2023 evaluation and a test evaluation with the new updates were all >=90% for genomic estimated breeding values (GEBV) and >=97% for genomic reliability (GREL) for all traits except for DA. The DA correlations were >=81% for GEBV and >=84 for GREL due to the largest change in h^2 which also impacted the variance-adjusted weights. Correlations suggest some variation, but the variance adjustments effectively capture the categorical trait of incidence in a linear model.