Data from a Nelore herd were used after adjustment of the weaning weight for 205 days of age, sex, age of dam, sire and weaning month and resulted into two groups of cows according to the in weaning weight of their calves (heavy and light groups). The least square means (LSM) for weaning weights were 163.21± 2,18kg and 134,44± 2.18kg, for heavy (H) and light (L) groups, with 41 animals each one. These animals were genotyped for DNA polymorphisms of the bovine somatotropin gene, using PCR-RFLP (polymerase chain reaction-restriction fragment length polymorphism). Amplification of a region between exons III and V of somatotropin gene allowed analysis of two restriction sites. All animals showed monomorphism for the V exon site, showing the (Leu-Leu) genotype. At intron 3 site, there were identified the 21+/- and 60 -/- genotypes, with 0.13 and 0.87 frequencies to (+) and (-) alleles, respectively. The calves from +/- counts was of 152.42± 4.41kg and of calves from -/- cows was 147.60± 2.61kg. Heavy and light groups were similar for the allelic frequencies. The dam’s genotype did not affect the weaning weight of the calves. This suggests the existence of another genetic or non-genetic factors with major magnitude.
Cattle; somatotropin; PCR; RFLP; genetic polymorphism