The association between the STAT1 g.3141C>T polymorphism and reproductive performance in high-yielding holstein-friesian dairy cows
In dairy cattle, selection programs have mainly focused on high milk production which led to significant improvements in yield. However, it has also caused serious problems in bovine fertility. Reproductive performance is increasing in popularity worldwide.
Therefore, this study aimed to evaluate the effects of g.3141C>T polymorphism of bovine STAT1 gene on reproductive traits in high-yielding Holstein-Friesian cows. The data of 4800 cows were used and the initial experimental population consisted of 500 purebred cows housed in three free-stall barns. All animals were fed the same diets and had the same management procedures.
The phenotypic traits analyzed in this study were total milk yield, 305-day milk yield, days open, the number of inseminations, and culling rates based on repeat-breeding. Body condition scores, lactation season, and lactation rank were also evaluated in statistical models. Initially, all of the cows were ranked by a selection index based on individual milk yield records and health traits. Next, a total of 75 cows were selected and genotyped for the STAT1 marker located in 3’UTR by the PCR-RFLP method.
Genotype-phenotype association analysis was carried out by the least-squares method as applied in a general linear model (GLM) procedure with Tukey’s test as a post-hoc comparison. The association between the cull rates and the genotypes was evaluated by Pearson’s chi-square test. Population genetics parameters including heterozygosity (He), homozygosity (Ho), number of effective alleles (Ne), and the polymorphic information content (PIC) were evaluated and the deviation from Hardy-Weinberg Equilibrium (HWE) was tested. Results revealed that g.3141C>T polymorphism exhibited admissible levels of population parameters (He=0.4801; Ne=1.9231) indicating that this marker is moderately informative for the selected population (PIC=0.3648).
There was a deviation from HWE (P<0.001). In GLM, the association between the STAT1 marker and the number of inseminations was found to be statistically significant (P<0.05). The TT animals were characterized by the highest number of inseminations (3.71±0.73). On the other hand, heterozygous animals were shown to be associated with desirable reproduction performance.
This is a critical result because the STAT1 g.3141C>T marker is included in many SNP-panels or SNP-chips for its previously reported effects on milk yield. To the best of our knowledge, this study has shown a novel effect of this STAT1 marker on the number of inseminations per conception. Considering the TT genotype has a frequency of 26.67%, ignoring this association can lead to a significant reproduction performance decrease on a herd basis. Moreover, there was a significant association between the STAT1 and cull rates (P<0.01). There was no association between the STAT1 and any other traits analyzed.
This study demonstrates novel effects of the STAT1 gene, and hence, may contribute to the adequate genotypic evaluation of dairy cattle reproduction performance.