Elsevier

Journal of Dairy Science

Volume 88, Issue 3, March 2005, Pages 1166-1177
Journal of Dairy Science

Article
Estimation of Genetic Parameters for Milk Fat Depression in Dairy Cattle

https://doi.org/10.3168/jds.S0022-0302(05)72783-1Get rights and content
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Abstract

The objective of this study was to apply reaction norm models to milk recording data to investigate genetic variation in and environmental sensitivity of susceptibility to milk fat depression (MFD). Data comprised 556,276 test-day records of 80,493 heifers in 1043 herds. Breeding values and genetic variances for fat percentage and fat yield were estimated by applying random regression models to average herd-test-day fat percentage. Genetic and permanent environmental correlations between fat yield expressed in different environments ranged, respectively, from 0.83 to 1.00 and from 0.29 to 1.00. Genetic and permanent environmental correlations between fat percentage expressed in different environments ranged, respectively, from 0.87 to 1.00 and from −0.05 to 0.99. Two traits were defined for MFD. The first trait reflected variation of milk fat percentage of animals within lactation after correction for year-season, herd-test-day, age-at-calving, and stage-of-lactation. This trait had an estimated heritability of about 5% and a genetic correlation between the fifth and 95th percentile of the data of 0.50. The second trait reflected the deviation of an animal's fat percentage on a test-day from its expected fat percentage based on fat percentage on the first test-day. This trait had an estimated heritability of about 4% and a genetic correlation between the fifth and 95th percentile of the data of 0.43. The correlation between estimated breeding values of sires for the 2 MFD traits was −0.3. Our results suggest that genetic variation in susceptibility to MFD is present and that selection for reduced susceptibility to MFD is possible.

Key words

milk fat depression
acidosis
environmental sensitivity
reaction norm model

Abbreviation key

AHTDF%
average herd-test-day fat percentage
BVM
bivariate repeatability model
MF%
milk fat percentage
MFD
milk fat depression
MFDLAC
milk fat depression trait defined on a lactation level
MFDTD
milk fat depression trait defined on a test-day level
RRM
random regression model

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