The present study aimed to evaluate the effects of hair coat on age at first calving (IPP) and calving interval (IEP) of Holstein cows managed under free stall with fans and sprinklers and to estimate genetic and phenotypic parameters for these traits. Data were analyzed by the least-squares method using a model that included the effects of year; season; origin of sire; sire within origin; number of inseminations; age (only for calving interval); percentage of black meshes; hair coat thickness; hair length; number of hair per unit area; hair diameter; effective transmissivity and reflectivity. Covariance components were estimated by REML using an Animal Model. Heritability estimates for IPP, IEP, percentage of black meshes, number of hair per unit area, hair coat thickness, hair length and hair diameter were 0.23±0.08, 0.19±0.10, 0.75±0.08, 0.05±0.04, 0.04±0.05, 0.36±0.09, and 0.63±0.08, respectively. Genetic correlation between hair diameter and IPP (IEP) was equal to -0.37±0.17 (-0.49±0.27). However, genetic correlations between IPP and hair thickness (-0.56±0.46), number of hair (-0.66±0.43) and black meshes (0.04±0.16) were unfavorable for jointly selection for sexual precocity and fitness to tropical environment. High values of heritability estimates and genetic correlations between diameter, IPP and IEP indicate that is possible to select for thickness of hair diameter and improve reproductive efficiency.
age at first calving; bovine; calving interval; fitness; genetic correlation; heritability
