The objectivesin this study were to compare alternative animal models for analysis of gestationperiod and verify if this trait has enough genetic variability to be includedin selection programs, by using heritability estimates and genetic correlationswith body weights at birth (BW) and at 12 months of age (W12), in a Canchimherd. Gestations of 2,889 calves, weight of 8,506 animals at birth and 6,372animals at 12 months of age were analyzed. Gestation period was studied as calf(GPC) and dam trait (GPD). Genetic parameters were estimatedby the restricted maximum likelihood method (REML). Four alternative animalmodels were tested in single trait analyses of GPC and GPD,considering fixed effects and combinations of three random effects. The likelihoodratio test was used to compare the models. Two-trait analyses were realizedbetween GPC and BW and between GLC and W12. Direct heritabilitiesof GPC varied from 0.22 to 0.41 and of GPD from 0.04 to0.07. Genetic correlation between GPC and BW was 0.65 and betweenGPC and W12 was 0.01. It is conclude that GP should be studied ascalf trait. The model with only direct additive effects and maternal permanentenvironmental may be used to genetic analysis of this trait, and this traitmay be used as an auxiliary selection criterion.
