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Logo of gseBioMed CentralBiomed Central Web Sitesearchsubmit a manuscriptregisterthis articleGenetics, Selection, Evolution : GSEJournal Front Page
 
Genet Sel Evol. 2008; 40(4): 333–357.
Published online Jul 15, 2008. doi:  10.1186/1297-9686-40-4-333
PMCID: PMC2674906
Exploration of lagged relationships between mastitis and milk yield in dairycows using a Bayesian structural equation Gaussian-threshold model
Xiao-Lin Wu,corresponding author1 Bjørg Heringstad,2 and Daniel Gianola1,2,3
1Department of Dairy Science, University of Wisconsin, Madison, WI 53706, USA
2Department of Animal and Aquacultural Sciences, Norwegian University of Life Sciences, 1432 Ås, Norway
3Department of Animal Sciences and Department of Biostatistics and Medical Bioinformatics, University of Wisconsin, Madison, WI 53706, USA
corresponding authorCorresponding author.
Xiao-Lin Wu: nickwu/at/ansci.wisc.edu
Received May 17, 2007; Accepted January 15, 2008.
Abstract
A Gaussian-threshold model is described under the general framework of structural equation models for inferring simultaneous and recursive relationships between binary and Gaussian characters, and estimating genetic parameters. Relationships between clinical mastitis (CM) and test-day milk yield (MY) in first-lactation Norwegian Red cows were examined using a recursive Gaussian-threshold model. For comparison, the data were also analyzed using a standard Gaussian-threshold, a multivariate linear model, and a recursive multivariate linear model. The first 180 days of lactation were arbitrarily divided into three periods of equal length, in order to investigate how these relationships evolve in the course of lactation. The recursive model showed negative within-period effects from (liability to) CM to test-day MY in all three lactation periods, and positive between-period effects from test-day MY to (liability to) CM in the following period. Estimates of recursive effects and of genetic parameters were time-dependent. The results suggested unfavorable effects of production on liability to mastitis, and dynamic relationships between mastitis and test-dayMYin the course of lactation. Fitting recursive effects had little influence on the estimation of genetic parameters. However, some differences were found in the estimates of heritability, genetic, and residual correlations, using different types of models (Gaussian-threshold vs. multivariate linear).
Keywords: Bayesian inference, mastitis, milk yield, structural equation model, threshold model
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