Article (Scientific journals)
Use of (co)variance functions to describe (co)variances for test day yield
Tijani, A.; Wiggans, G. R.; Van Tassell, C. P. et al.
1999In Journal of Dairy Science, 82 (1), p. 226.e1-226.e14
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Keywords :
(co)variance function; test day model; variance component estimation
Abstract :
[en] (Co)variance functions for milk, fat, and protein yields during first lactation were developed from (co)variance components for four lactation stages of 75 d each that had been previously estimated using test day data from 17,190 Holstein cows from 37 herds in Pennsylvania and Wisconsin. The (co)variance functions were evaluated at 18, 43, 68, 93, 118, 143, 168, 193, 218, 243, 268, and 293 d in milk. Residuals were subdivided into time-dependent (permanent) and temporary environmental effects for estimation of (co)variance functions. Mean relative variance (portion of total variance) for time-dependent environmental effects was 0.50 for milk yield and 0.51 for fat and protein yields. Heritability estimates generally were lower at the start and end of lactation and were highest for milk yield; mean heritability estimates were 0.20 for milk, 0.16 for fat, and 0.17 for protein yields. Phenotypic and genetic correlations were higher between milk and protein yields than between milk and fat yields. Within yield traits, genetic correlations declined from ≥0.93 for adjacent lactation stages to 0.52 for milk, 0.58 for fat, and 0.60 for protein between initial and final lactation stages. Within lactation stage, mean genetic correlations were 0.40 between milk and fat yields, 0.78 between milk and protein yields, and 0.55 between fat and protein yields; corresponding mean phenotypic correlations were 0.65, 0.92, and 0.67. The (co)variance function methodology allowed interpolation and extension of (co)variance components over the entire lactation.
Disciplines :
Genetics & genetic processes
Animal production & animal husbandry
Author, co-author :
Tijani, A.
Wiggans, G. R.
Van Tassell, C. P.
Philpot, J. C.
Gengler, Nicolas  ;  Université de Liège - ULiège > Gembloux Agro-Bio Tech > Gembloux Agro-Bio Tech
Language :
English
Title :
Use of (co)variance functions to describe (co)variances for test day yield
Publication date :
January 1999
Journal title :
Journal of Dairy Science
ISSN :
0022-0302
eISSN :
1525-3198
Publisher :
American Dairy Science Association, Champaign, United States - Illinois
Volume :
82
Issue :
1
Pages :
226.e1-226.e14
Peer reviewed :
Peer Reviewed verified by ORBi
Available on ORBi :
since 17 September 2009

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