Abstract
The objectives of the present study were to estimate the allele and genotype frequencies of the GH1/Alu I and POU1F1/Hinf I polymorphisms in beef cattle belonging to different genetic groups and to determine the effects of these polymorphisms on growth and carcass traits in cattle submitted to feedlot management, an intensive production model. Genotyping was performed on 384 animals, including 79 Nellore, 30 Canchim (5/8 Charolais + 3/8 Zebu), 30 Simmental x Nellore crossbred and 245 Angus x Nellore crossbred cattle. Body weight, weight gain, dressing percentage, Longissimus dorsi area and backfat thickness were fitted using the General Linear Model (GLM) procedure of the SAS program and the least square means of the genotypes were compared using the F test. The results showed significant associations between the LL genotype of the GH1/Alu I polymorphism and higher weight gain and body weight at slaughter (p < 0.05). The POU1F1/Hinf I polymorphism did not have any effect on the growth and carcass traits analyzed.
Highlights
Most traits of economic interest are of a quantitative nature and are controlled by a large number of genes which each contribute a small effect to the trait, the loci responsible for such traits being known as quantitative trait loci (QTL)
The GH1/Alu I polymorphism identified by Lucy et al (1991) consists of a cytosine to guanine exchange at codon 127 in the GH1 gene and the substitution of the amino acid leucine (L allele) by valine (V allele) to produce different forms of the growth hormone which can differ in receptor-binding efficiency and modify physiologic processes and produce different phenotypes
The L allele frequencies obtained were similar to results reported in the literature which showed a fixation of this allele in Zebu breeds (Kemenes et al, 1999) and its predominance in the taurine breeds Charolais (Kemenes et al, 1999), Piedmontese (Di Stasio et al, 2002), Simmental and Angus (Vasconcellos et al, 2003), with frequencies of 0.72, 0.72, 0.82 and 0.77, respectively
Summary
Most traits of economic interest are of a quantitative nature and are controlled by a large number of genes which each contribute a small effect to the trait, the loci responsible for such traits being known as quantitative trait loci (QTL). The somatotrophic axis play a key role in the regulation of the metabolism and physiology of mammalian growth and essentially consists of growth hormone (GH), insulin-like growth factors 1 and 2 (IGF-1 and IGF-2) and their associated binding proteins (BP) and receptors (R), i.e. IGFBP, GHR, IGF-1R and IGF-2R. The GH1 gene codifies for circulating growth hormone which binds to the extracellular domain of specific transmembrane growth hormone receptors (GHR) which are expressed in various tissues, especially liver-tissue. This process is the signal for a cascade of intracellular metabolic events culminating in the production of IGF-1 by the target tissues, of which liver-tissue is the most important (Renaville et al, 2002)
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