Efeitos dos polimorfismos T945M, C305T E BM1500 em caracteres produtivos e reprodutivos em fêmeas nelore

Abstract

Body weight in heifers be related to the onset of puberty and consequently to the onset of the reproductive cycle. The reproduction is a parameter of great return in beef cattle, because it provides greater availability of animals, therefore, greater profitability. Zebu animals correspond to the largest proportion of Brazilian beef cattle and the zebu females tend to reach their sexual maturity in a late period. Thus, the identification of genes and polymorphisms that may be involved with higher reproductive performance is relevant to identify such condition. The aim of this study was to evaluate two SNP markers in the leptin gene (C305T) and in the leptin receptor gene (T954M), and the one microsatellite marker (BM1500) located close to the leptin gene and to seek for associations with the body weight productive trait and reproductive traits of age at first calving (AFC), calving interval (CI) and reproductive efficiency (RE) in a group of Nellore cattle. DNA extraction from 138 females was performed, followed by amplification of the SNP T945M and C305T and BM1500 microsatellite. After genotyping the data obtained were analyzed for population diversity using Cervus 3.0 software. The study of association between the genotypes of each marker with the characteristics weight, AFC, CI and RE, was performed using the PROC MIXED procedure of the SAS® software. For the longitudinal measures of weight, the non-linear Gompertz model was used to obtain the parameters of the growth curve and after that, the Lack of Fit test was performed to compare the fit of the complete model with the reduced model. Both SNP markers presented two allelic variations, C and T, and both CC genotypes had the highest frequencies, 0.73 and 0.67, for T945M and C305T, respectively. The BM1500 microsatellite presented three alleles, 149, 147 and 138, with a higher genotypic frequency for 147/147 (0.55). The association analyses between all markers and reproductive traits and between the SNP markers and the body weight trait were not significant (p < 0.05). However, for the BM1500 microsatellite, the effect of the allele 138 (p = 0.0383) on body weight was observed, with the growth curve for such allele (Lack of Fit Test = 0.01) being related to low asymptotic weight. The low allele frequency (0.06) for this allele and absence of homozygous genotype indicate that it was eliminated from the herd by selection processes, once its relation with the increase in body weight was negative. These results could help cattle producers in their selection processes through marker-assisted selection, as the BM1500 microsatellite proved to be efficient in providing information about the body weight of Nellore females.