Polimorfismo no gene do hormônio liberador do hormônio do crescimento e seu efeito nos índices produtivos e reprodutivos em bovinos da raça girolando

Abstract

Genomic polymorphism investigations can contribute to increase available Information about the variability of the quantitative characteristics. Considering the important physiological functions carried out by the genes which participate in the Growth Hormone expression in several phenotypic characteristics of economic interest in milk cattle, this study purposed to investigate the association between a polymorphism in the Growth Hormone Releasing Hormone (GHRH) gene and the productive and reproductive indexes: milk production, daily average milk production, lactation duration and delivery interval average, in Girolando breed cattle. In order to genotype the 453 females, the PCR-RFLP technique (Polymerase Chain Reaction - Restriction Fragment Length Polymorphism) was used. The restriction of the 455 bp amplicon, with the Haelll enzyme, revealed a polymorphism with two alleles: A allele, presenting the fragments 317, 83 and 55 bp and B allele, with the fragments 196, 121, 83 and 55 bp. Genotypic frequencies obtained were 2.87%, 36.64% and 60.49% for the AA, AB and BB genotypes, respectively, being the A allele frequency, 21.19% and the B allele frequency, 78.81%. 299 animais were used for the statistical analysis and there was no significant difference (p> 0.05) among genotypes with regards to milk production, daily average milk production and delivery interval average. Regarding the lactation duration, the AB genotype showed itself superior to the BB genotype (p< 0.01) and the mean effect of an allelic substitution was of 2 days, being the A allele the favorable one. With this result, it can be suggested the use of AA or AB bulls in the crosses aiming to increase the frequency of the A allele and, consequently, the lactation duration average by two days in the cattle.