Journal ArticleDOI
Use of test day yields for genetic evaluation of dairy sires and cows
Ewa Ptak,L.R. Schaeffer +1 more
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TLDR
Genetic evaluations based on test day yields offer many advantages over those based on 305-day lactations including better modeling of factors affecting yields, no need to extend records, and possibly greater accuracy of evaluations.About:
This article is published in Livestock Production Science.The article was published on 1993-03-01. It has received 282 citations till now. The article focuses on the topics: Dairy cattle.read more
Citations
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Journal ArticleDOI
Estimates of Genetic Parameters for a Test Day Model with Random Regressions for Yield Traits of First Lactation Holsteins
Janusz Jamrozik,L.R. Schaeffer +1 more
TL;DR: A model that contains both fixed and random linear regressions is described for analyzing test day records of dairy cows, and genetic correlations between daily yields were higher as the interval between tests decreased, and correlations of daily yields with 305-d yields were greatest during midlactation.
Journal ArticleDOI
Genetic Component of Heat Stress in Dairy Cattle, Parameter Estimation
O. Ravagnolo,Ignacy Misztal +1 more
TL;DR: The authors' data included 119,205 first-parity, test-day records from 15,002 Holsteins in 134 Georgia farms with temperature and humidity data from 21 weather stations throughout Georgia, finding joint selection for heat tolerance and production is possible.
Journal ArticleDOI
Estimation of genetic and phenotypic covariance functions for longitudinal or ‘repeated’ records by restricted maximum likelihood
Karin Meyer,William G. Hill +1 more
TL;DR: In this article, the covariance matrices for traits with many, potentially infinitely many, records in which the covariances are defined as a function of age or time are presented.
Journal ArticleDOI
Genetic Evaluation of Dairy Cattle Using Test Day Yields and Random Regression Model
TL;DR: A model for analyzing test day records that contains both fixed and random regression coefficients was applied to the genetic evaluation of first lactation data for Canadian Holstein dairy cows, finding a range of estimated breeding values for various parts of the lactation.
Journal ArticleDOI
Experience with a Test-Day Model
TL;DR: The Canadian Test-Day Model is a 12-trait random regression animal model in which traits are milk, fat, and protein test-day yields, and somatic cell scores on test days within each of first three lactations.
References
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Journal ArticleDOI
Accounting for covariances among test day milk yields in dairy cows
T. E. Ali,L.R. Schaeffer +1 more
TL;DR: Better predictions were observed when covariances among test-day yields were ignored while models could be ranked regression model, gamma function, and inverse quadratic polynomial function.
Journal ArticleDOI
Factors affecting the shape of the lactation curve in cattle
TL;DR: In a sample of 859 Friesian lactations recorded during 1964–65 daily yield was depressed during the winter months and stimulated during the spring to an extent which was independent of the stage of lactation.
Journal ArticleDOI
Estimating milk, fat, and protein lactation curves with a test day model.
TL;DR: Differences between lactation curves for the two seasons were slight, suggesting that most observed seasonal differences are caused by seasonal productivity accounted for by herd test date effects.
Journal ArticleDOI
Estimates of genetic parameters for first lactation test day production of Australian black and white cows
TL;DR: In this paper, the authors estimated heritability and genetic and phenotypic correlations for first-lactation test day production, based on a total of 502 453 test day records.
Journal ArticleDOI
Comparison of different methods of predicting 305-day milk yield using means calculated from within-herd lactation curves
TL;DR: A procedure for estimation of the means is presented and single regression, multiple regression (MR), and factor analysis (FA) models for prediction are compared and Type II means resulted in a more precise adjustment.
Related Papers (5)
Estimates of Genetic Parameters for a Test Day Model with Random Regressions for Yield Traits of First Lactation Holsteins
Janusz Jamrozik,L.R. Schaeffer +1 more