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Abstract
Animals that are robust to environmental changes are desirable in the current dairy industry. Genetic differences in microenvironmental sensitivity can be studied through heterogeneity of residual variance between animals. However, residual variance between animals is usually assumed to be homogeneous in traditional genetic evaluations. The aim of this study was to investigate genetic heterogeneity of residual variance by estimating variance components in residual variance for milk yield, somatic cell score, contents in milk (g/dL) of 2 groups of milk fatty acids (i.e., saturated and unsaturated fatty acids), and the content in milk of one individual fatty acid (i.e., oleic acid, C18:1 cis9), for firstparity Holstein cows in the Walloon Region of Belgium. A total of 146,027 testday records from 26,887 cows in 747 herds were available. All cows had at least 3 records and a known sire. These sires had at least 10 cows with records and each herd × testday had at least 5 cows. The 5 traits were analyzed separately based on fixed lactation curve and random regression testday models for the mean. Estimation of variance components was performed by running iteratively expectation maximizationREML algorithm by the implementation of double hierarchical generalized linear models. Based on fixed lactation curve testday mean models, heritability for residual variances ranged between 1.01 × 103 and 4.17 × 103 for all traits. The genetic standard deviation in residual variance (i.e., approximately the genetic coefficient of variation of residual variance) ranged between 0.12 and 0.17. Therefore, some genetic variance in microenvironmental sensitivity existed in the Walloon Holstein dairy cattle for the 5 studied traits. The standard deviations due to herd × testday and permanent environment in residual variance ranged between 0.36 and 0.45 for herd × testday effect and between 0.55 and 0.97 for permanent environmental effect. Therefore, nongenetic effects also contributed substantially to microenvironmental sensitivity. Addition of random regressions to the mean model did not reduce heterogeneity in residual variance and that genetic heterogeneity of residual variance was not simply an effect of an incomplete mean model.
Original language  English 

Pages (fromto)  59775990 
Journal  Journal of Dairy Science 
Volume  96 
Issue number  9 
DOIs  
Publication status  Published  2013 
Keywords
 generalized linearmodels
 residual variance
 breeding values
 fattyacids
 production traits
 bovinemilk
 heterogeneity
 variability
 prediction
 components
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 1 Finished

ROBUSTMILK: Innovative and Practical Breeding Tools for Improved Dairy Products from More Robust Dairy Cattle
1/04/08 → 30/09/12
Project: EU research project