Effect of pregnancy on production traits of Canadian Holstein cows
- 1 June 2009
- journal article
- Published by American Dairy Science Association in Journal of Dairy Science
- Vol. 92 (6), 2947-2959
- https://doi.org/10.3168/jds.2008-1782
Abstract
Seven test-day models with different ways of accounting for the effect of pregnancy on production traits were compared by their residual variance, rank correlations of estimated breeding values of bulls and cows and number of nonpregnant cows in the top 500 for milk yield and milk persistency. Data were 22,546,696 first-parity test-day milk, fat, and protein yields and somatic cell score records of 2,677,862 Canadian Holstein heifers calved between 1988 and 2006. The first model fitted separate lactation curves to 8 days open classes and 1 curve to a nonpregnant cow class. Two other models adjusted for pregnancy by fitting the effect of month of pregnancy or stage of pregnancy. One model fitted regression on days pregnant. The remaining 3 models fitted interactions between stage of pregnancy and stage of lactation when conception occurred using either regression on days pregnant nested within days open or classes for specific stage of pregnancy and stage of lactation combination. All models were contrasted to a model without any adjustment for the effect of pregnancy. Both models that accounted for the effect of pregnancy and the model without the effect of pregnancy had similar residual variance. Adjusting for the effect of pregnancy did not cause reranking of sires for estimated breeding values for 305-d yield and persistency but influenced ranking of cows. Models that used days open for the effect of pregnancy overestimated breeding values of nonpregnant cows and cows with shorter days open. No interaction was found between stage of pregnancy and stage of lactation. Month of pregnancy and stage of pregnancy models, compared with the model without the effect of pregnancy, decreased overestimation of breeding values of nonpregnant cows and did not overestimate breeding values of cows with short days open like models fitting days open. Month of pregnancy and stage of pregnancy models are recommended for estimation of adjustment factors for the effect of pregnancy on production traits.Keywords
Funding Information
- DairyGen Council of Canadian Dairy Network
- NSERC of Canada
This publication has 19 references indexed in Scilit:
- Comparison of Random Regression Models with Legendre Polynomials and Linear Splines for Production Traits and Somatic Cell Score of Canadian Holstein CowsJournal of Dairy Science, 2008
- Environmental effects on lactation curves included in a test-day model genetic evaluationAnimal, 2008
- Major Advances Associated with Hormone and Growth Factor Regulation of Mammary Growth and Lactation in Dairy CowsJournal of Dairy Science, 2006
- Effects of pregnancy on daily milk yield of Holstein–Friesian dairy cattleLivestock Production Science, 2004
- Modeling Lactation Curves and Estimation of Genetic Parameters for First Lactation Test-Day Records of French Holstein CowsJournal of Dairy Science, 2003
- Genetic and environmental relationship among calving interval, survival, persistency of milk yield and somatic cell count in dairy cattleLivestock Production Science, 2003
- Estimating Effects of Permanent Environment, Lactation Stage, Age, and Pregnancy on Test-Day YieldJournal of Dairy Science, 2002
- Genetic Parameters and Trends of Milk, Fat, Days Open, and Body Weight After Calving in North Carolina Experimental HerdsJournal of Dairy Science, 2000
- Growth and Accretion of Energy and Protein in the Gravid Uterus During Late Pregnancy in Holstein CowsJournal of Dairy Science, 1995
- Modelling the effect of the stage of pregnancy on dairy cows' milk yieldAnimal Science, 1995