TAILIEUCHUNG - Báo cáo sinh học: "Modelling the growth curve of Maine-Anjou beef cattle using heteroskedastic random coefficients models"

Tuyển tập các báo cáo nghiên cứu về sinh học được đăng trên tạp chí sinh học thế giới đề tài: Modelling the growth curve of Maine-Anjou beef cattle using heteroskedastic random coefficients models | 423 Genet Sei. Evol. 34 2002 423-445 INRA EDP Sciences 2002 DOI gse 2002016 Original article Modelling the growth curve of Maine-Anjou beef cattle using heteroskedastic random coefficients models Christèle Robert-Graniéa Barbara Heudeb Jean-Louis Foulleyb a Station d amelioration génétique des animaux Institut national de la recherche agronomique BP 27 31326 Castanet-Tolosan France b Station de génétique quantitative et appliquée Institut national de la recherche agronomique 78352 Jouy-en-Josas Cedex France Received 6 April 2001 accepted 7 January 2002 Abstract - a heteroskedastic random coefficients model was described for analyzing weight performances between the 100th and the 650th days of age of Maine-Anjou beef cattle. This model contained both fixed effects random linear regression and heterogeneous variance components. The objective of this study was to analyze the difference of growth curves between animals born as twin and single bull calves. The method was based on log-linear models for residual and individual variances expressed as functions of explanatory variables. An expectation-maximization EM algorithm was proposed for calculating restricted maximum likelihood REML estimates of the residual and individual components of variances and covariances. Likelihood ratio tests were used to assess hypotheses about parameters of this model. Growth of Maine-Anjou cattle was described by a third order regression on age for a mean growth curve two correlated random effects for the individual variability and independent errors. Three sources of heterogeneity of residual variances were detected. The difference of weight performance between bulls born as single and twin bull calves was estimated to be equal to about 15 kg for the growth period considered. heteroskedastic random coefficient model EM-REML robust estimators growth curve Maine-Anjou breed Correspondence and reprints E-mail robert@ 424 c. Robert-Granié et al. 1. .

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