Quantitative genetic analysis of morphological and functional traits in Nelore cattle

Morphological and functional problems can determine that top animals of commercial breeding programs are ineligible for receiving an official certificate of genetic superiority (CEIP), possibly leading to economic losses. The aim of this study was to estimate genetic parameters of morphological and functional traits in Nelore cattle, to assess the feasibility of considering them as selection criteria. Phenotypic records from a beef cattle breeding program were obtained for the following traits: feet and legs problems, a binary trait evaluated at weaning (FL_W) and yearling (FL_Y), and by a final inspection of candidates to receive the CEIP (FL_R); prognathism/agnathism problems, evaluated at weaning (BO_W) and yearling (BO_Y); nasal deviation, evaluated at weaning (ND_W) and yearling (ND_Y); depigmentation, evaluated at weaning (NP_W) and yearling (NP_Y); testicular problems, a binary trait evaluated at yearling (T_Y); racial characterization (RC); navel/prepuce, evaluated at weaning (N_W) and yearling (N_Y). Estimates of (co)variance components were obtained for the different traits through Bayesian analysis by fitting single-trait threshold animal models, using THRGIBBS1F90 software (Misztal, 2015). Considerable phenotypic incidence of problems associated to morphological and functional traits was verified, being FL_R and N_Y the traits with greatest incidence of problems (about 10%). Heritability estimates suggest important influence of additive genetic effects on all traits analyzed. The greatest posterior means (highest posterior density interval at 95%) of heritability estimates were verified for depigmentation, above 0.70 (0.584 to 0.829). The heritability estimates to racial characterization, navel and feet and legs were from moderate to high magnitude. Lower heritabiltiy estimates were obtained for the remaining traits, ranging between 0.15 (0.08 to 0.23) for FL_Y and T_Y; and 0.23 (0.12 to 0.37) for ND_W and BO_Y. The results indicate that reduction of incidence of morphological and functional problems can be achieved through selection and assortative mating in this population.