Dairy cattle

Genetic parameters for traits derived from measures of electrical conductivity collected by automatic milking systems and their correlations with clinical mastitis in Holstein cattle

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Abstract

Genetic selection for mastitis (MAST) resistance in dairy cattle utilizes direct selection on clinical cases and indirect selection via somatic cell score (SCS). Despite these efforts, mastitis remains a major health and welfare concern, with significant economic impacts. Precision technologies like automatic milking systems (AMS) can capture novel phenotypes that could enhance indirect selection for MAST resistance at a lower cost and higher frequency compared to existing traits. Specifically, electrical conductivity (COND) measured at individual milkings by AMS may be valuable for this effort. While COND shows promise for improving selection for MAST resistance, consensus on trait derivations among previous research is lacking, and few genetic correlations with MAST and SCS have been estimated. Therefore, the objectives of this study were to 1) derive multiple COND traits from quarter-level COND records and 2) estimate variance components for these derived traits and their covariance components with MAST and SCS. Quarter-level COND was collected at every milking on 7,157 Holstein cows milked with AMS. Additionally, records for MAST and test-day SCS were available for an expanded population that was milked with both AMS and traditional parlors (23,001 and 18,664 cows, respectively). Four traits were derived by combining quarter-level COND records collected at each milking: average electrical conductivity (AVGCOND), inter-quarter ratio of electrical conductivity (IQRCOND), maximum electrical conductivity (MAXCOND), and range of electrical conductivity (RNGCOND). These visit-level traits were then summarized into daily values for subsequent analyses, with AVGCOND, IQRCOND, and RNGCOND calculated as the daily average and MAXCOND as the daily maximum. Also, data was analyzed separately by lactation: 1, 2, or 3+. Pedigree data for 53,186 individuals, and genotype data for 6,938 individuals, imputed to 50,886 SNP, was used for analyses. (Co)variance components were estimated using single-step GBLUP and linear animal models with REML. Estimates of heritability for derived COND traits ranged from 0.01 ± < 0.01 for RNGCOND in lactation 3+ to 0.52 ± 0.02 for AVGCOND in lactation 1. Estimates of genetic correlation between the derived COND traits and MAST ranged from 0.30 ± 0.08 for AVGCOND and MAST in lactation 3+ to 0.81 ± for 0.07 for RNGCOND and MAST in lactation 2, while estimates of genetic correlation between the derived COND traits and SCS ranged from 0.03 ± 0.06 for RNGCOND and SCS in lactation 1 and 0.65 ± 0.04 for MAXCOND and SCS in lactation 3+. Our results show that traits derived from records of COND are heritable and have moderate to high genetic correlations with MAST, while having low to high genetic correlations with SCS. This means that they can provide a complementary approach to improving selection for MAST resistance while also offering a cost-effective method that can be collected more frequently than existing traits.

Keywords: 2026

How to Cite:

Maskal, J., Chen, S. & Brito, L., (2026) “Genetic parameters for traits derived from measures of electrical conductivity collected by automatic milking systems and their correlations with clinical mastitis in Holstein cattle”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2284140. doi: https://doi.org/10.31274/wcgalp.23550

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