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J. Dairy Sci. 89:779-781
© American Dairy Science Association, 2006.

Short Communication: Genetic Correlation Between Test-Day Electrical Conductivity of Milk and Mastitis

E. Norberg*,1, G. W. Rogers{dagger}, J. Ødegård{ddagger}, J. B. Cooper{dagger} and P. Madsen*

* Department of Genetics and Biotechnology, Danish Institute of Agricultural Sciences, Research Center Foulum, P.O. Box 50, DK-8830 Tjele, Denmark
{dagger} Department of Animal Science, University of Tennessee, Knoxville 37996
{ddagger} Department of Animal and Aquacultural Sciences, Norwegian University of Life Sciences, P.O. Box 5003, N-1432 Ås, Norway

1 Corresponding author: Elise.Norberg{at}agrsci.dk

Electrical conductivity (EC) of milk is an indicator of mastitis. If EC shows genetic variation and is genetically correlated to mastitis, it could be used in a breeding program that includes selection for improved mastitis resistance. In this study, daily records of EC and mastitis from about 1,500 Holstein cows were analyzed. A bivariate animal model was used for estimation of (co)variance components, including fixed effects of age of calving, herd-test-day, and days in milk, in addition to random additive genetic effects and permanent environmental effects. For EC, the estimated heritability was moderate (0.22 to 0.39), whereas for mastitis, the heritability was low (0.013). The genetic correlation between EC and mastitis was estimated to be 0.75, and genetic improvement of mastitis resistance should be feasible through selection for reduced EC.

Key Words: dairy cattle • mastitis • electrical conductivity • genetic correlation






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