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Random regression test-day model for clinical mastitis: genetic parameters, model comparison, and correlations with
Journal of Dairy Science
|April 16, 2014
Summary
This study analyzed genetic factors influencing clinical mastitis (CM) and milk production in Holstein cows using random regression models. Results show moderate genetic correlations between CM and somatic cell score, suggesting potential for simultaneous genetic improvement in udder health and yield.
Area of Science:
- Animal Genetics
- Dairy Science
- Quantitative Genetics
Background:
- Clinical mastitis (CM) is a significant disease in dairy cattle, impacting animal welfare and economic returns.
- Understanding the genetic basis of CM and its relationship with production traits is crucial for effective breeding strategies.
- Previous studies often used simpler models, potentially limiting the accurate estimation of genetic parameters over lactation.
Purpose of the Study:
- To estimate genetic (co)variance components for binary clinical mastitis (CM), test-day protein yield, and udder health traits using random regression models (RRM).
- To investigate the genetic correlations between CM, somatic cell score (SCS), and protein yield across different stages of lactation.
- To compare estimated breeding values (EBVs) for CM derived from RRM with those from traditional models and udder type traits.
Main Methods:
- Utilized a large dataset of 26,651 Holstein cows from 15 herds, including test-day production, CM, and udder type data (2007-2012).
- Applied bivariate threshold-linear random regression models to analyze longitudinal data for CM, protein yield, and SCS.
- Calculated heritabilities, genetic correlations between traits over lactation, and correlations between RRM-derived EBVs and official EBVs for udder type traits.
Main Results:
- Heritability for liability to CM was approximately 0.15 throughout lactation, slightly higher than for SCS.
- Moderate to high daily genetic correlations (around 0.70) were observed between CM and SCS, decreasing towards the end of lactation.
- Low to moderate genetic correlations between CM and protein yield were found, with no pronounced genetic antagonism, and RRM-EBVs showed moderate correlations with udder type traits.
Conclusions:
- Threshold RRM are suitable for routine genetic evaluation of CM, enabling selection for specific lactation stages.
- Selection based on RRM for CM can lead to higher genetic gains compared to strategies using indicator traits like SCS or type traits.
- The findings support the integration of RRM into breeding programs to improve both udder health and milk production simultaneously.
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