Abstract
Research to assess the effect of single genes on reproductive traits in bovine species is imperative to elucidate genes' functions and acquire a better perspective of quantitative traits. The present study was undertaken to characterize genetic diversity in the bovine growth hormone (GH) gene in a population of 410 Holstein dairy cows in Tunisia. The analyses were based on single nucleotide polymorphisms, and GH-AluI and GH-MspI detections and genotyping were carried out using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. Data were analyzed using a mixed linear model with the MIXED procedure to reveal the possible effect of GH genotypes on reproductive traits. The frequency data of AluI(L//V) and MspI(//) alleles were 87.04//12.96 and 70.06//29.94, respectively. The distribution of the frequency of GH genotypes for LL/LV/VV and (/)//(/)//(/) were 77.75//18.59//3.66 and 15.37//29.13//55.50, respectively. The results of the statistical analyses proved that GH-AluI showed a substantial favorable effect on exanimate traits except for the age at first calving; however, only a suggestive effect of GH-MspI on the calving interval (CI) and the days open (DI) was found. The homozygous LL genotype seemed to be advantageous with respect to the CI and the DI compared with LV and VV genotypes. Heterozygous MspI(/) cows tended to have a longer CI and DI than MspI(/) and MspI(/) cows, but the difference was not statistically significant. A significant effect of different GH-AluI–MspI combined genotypes was found on the number of inseminations per conception, the CI and the DI, and the LL/– combined genotype seemed to be associated with better reproductive performance. Based on these results, the LL genotype of the GH locus can be considered to be a favorable genotype for reproductive traits in Holstein dairy cattle, although these findings need to be confirmed by further research before polymorphisms can be used in a marker-assisted selection program.
Highlights
The availability of dense genomic information has increased genome-wide association research for quantitative traits in bovine species
Growth hormone (GH) is an anabolic hormone synthesized and secreted by the somatotroph cells, it is a major regulator of postnatal growth and metabolism in mammals, and it plays an important role in lactation, protein, lipid and carbohydrate metabolism, tissue growth, and fertility in cows (Akers, 2006; Lucy, 2008; Thidar et al, 2008)
The 428 and 329 pb fragments from the GH gene were characterized and successfully amplified from the DNA of each sample; this indicated a strong conservation of the DNA sequence existing in cattle
Summary
The availability of dense genomic information has increased genome-wide association research for quantitative traits in bovine species. Fertility is considered to be a functional polygenic trait controlled by numerous genetic loci and biased by environmental factors. Linked candidate genes of the encoding loci are searched to optimize reproductive performance. Growth hormone (GH) belongs to a family of somatolactogenic hormones which include placental lactogen, prolactin and anthers hematopoietic growth factors (Cosman et al, 1990). GH is an anabolic hormone synthesized and secreted by the somatotroph cells, it is a major regulator of postnatal growth and metabolism in mammals, and it plays an important role in lactation, protein, lipid and carbohydrate metabolism, tissue growth, and fertility in cows (Akers, 2006; Lucy, 2008; Thidar et al, 2008). The growth promoting and metabolic actions of GH are generally mediated
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