Influência do gene do hormônio do crescimento em características quantitativas de bovinos de leite

Abstract

The latest molecular biology technologies have made it possible to study DNA polymorphism and its relationship with quantitative characteristics of economic interest in dairy cattle. Growth hormone (GH) was used as a molecular marker to study its effect on quantitative characteristics, such as total milk production (PT), lactation days (DL), total fat production (GT) and fat percentage (PG) in dairy cattle. A total of 116 animals, 63 crossbred from Gir with Dutch and 53 purebred from the Dutch breed, were genotyped for GH and the genotypes used for the linkage study with quantitative characteristics. The animals were chosen at random in regions of the Triângulo Mineiro and the north of the state of São Paulo with similar conditions of sanitary and nutritional management, and all with official data on the first lactation. Optimal conditions for GH amplification included 200 ng of DNA, 1 mM MgCL, 8 nmoles of dNTPs, 8 pmoles of primers and 2 units of Taq polymerase, under 94 ° C of initial denaturation for 10 minutes, followed by 34 cycles at 94 ° C per minute for denaturation, 60 ° C per minute for annealing, 72 ° C per minute for extension, followed by a final extension of 10 minutes. The frequency of the C allele in the pure animals was 0.5755 versus 0.4444 in the crossbred animals. AVIII The frequency of the CC genotype in pure animals was also higher when compared to crossbred animals, being 0.3396 and 0.2063, respectively. The individuals homozygous for the C allele were characterized by 4 fragments, 526, 193, 109 and 63 pairs of bands (bp), while the homozygotes for the D allele lose a restriction site for the Msp I enzyme within intron 3 of the gene, producing 3 fragments of 635, 193 and 63 bp. Heterozygous animals all show band patterns. Statistical analysis showed significant differences (P <0.01) in total milk production, the highest for the CC genotype and the lowest for the DD genotype. The pure animals were superior to the crossed ones in their averages for days of lactation, total production of milk and fat. In the analysis of the effect of allelic substitution, we found the formula y = -386.5x + 5615.7 with x representing the genotypes CC = 0, CD = 1 and DD = 2.