Genetic analysis for scrotal circumference in Canchim beef cattle.
Scrotal circumference (SC) has been used as selection criteria in beef cattle breeding programs due to the ease of measurement and favorable genetic associations with female reproductive traits, such as age at puberty. The aim of this study was to estimate genetic parameters using different models for SC at weaning (SCW), at 365 days (SC365), and at 550 days (SC550) of age in Canchim cattle. Embrapa Southeast Livestock provided the data used in this study. A total of 1,046, 1,171,and 1,054 records of SCW, SC365, and SC550, respectively, from animals born from 1986 to 2013 were used. The genetic parameters were estimated by the restricted maximum likelihood method under an animal model. The Wombat software was used to performthe single-trait analyses. All models included the fixed effects of contemporary group (season and year of birth and genetic group for SCW and SC365; and year of birth for SC550) and the age at measurement as the linear covariate. Four genetic models with different random effects were considered: i. Additive genetic direct and residual;ii. Additive genetic direct, maternal genetic, and residual; iii. Additive genetic direct, maternal permanent environment, and residual; and iv. Additive genetic direct, maternal genetic, maternal permanent environment, and residual.The likelihood ratio test was applied () to choose the most suitable animal model for each trait. The direct heritabilities (h2) estimates ranged from 0.21?0.06 to 0.24?0.07 for SCW, from 0.28?0.08 to 0.41?0.07 for SC365, and from 0.34?0.08 to 0.52?0.09 for SC550. The maternal h2 estimates were0.12?0.04, 0.14?0.04, and 0.17?0.05 for SCW, SC365, and SC550, respectively. The proportion of maternal permanent environment variance to total variance ranged from 0.00 to 0.15?0.04 for all SC ages. The model including the additive genetic direct and maternal genetic effects was the most indicated for genetic evaluation in Canchim cattle at the studied ages. The additive genetic variance component reduced significantly (P<0.05) with the inclusion of maternal genetic effect, resulting in reduced direct heritability estimates. The genetic maternal effect should be included in genetic evaluation of Canchim cattle for SC measurements at different ages.