Evaluation of the association between polymorphism in Interleukin 2 and Interleukin 10 genes with reproductive traits in Holstein cattle

Reproductive efficiency is one of the most important factors influencing dairy cow performance. In the present study, relationship between the polymorphism in interleukin 2 (IL-2: exon 6) and interleukin 10 (IL-10: exon 5) genes with reproductive characteristics including days open, calving interval, days from calving to first duty, gestation period, Service result, stillbirth and calving ease was examined.

In the present study, the relationship between interleukin 2 and interleukin-10 as two candidate genes with some important reproductive traits in Holstein dairy cows was investigated by means of selective genotyping. Individuals were selected based on their open door residuals obtained from mixed models. In the model used, the effects of year of birth, year of calving, time of calving and lactation were taken into account as fixed effects, and the random effects of the animal and the covariate effect of milk yield were also included in the model. A total of 194 cows, 97 of which were individual cows, were selected from both tails of the residual value distribution. The DNA was extracted using a modified salting out procedure. Polymerase chain reactions (PCR) using specific primers were implemented to amplify fragments of 172 bp and 325 bp of IL-2 and IL-10, respectively. Different banding patterns were identified using the PCR-SSCP technique. The Cox test in SAS was used to examine the association between banding patterns with open days, calving interval, days from calving to first service, gestation duration. The logistics regression was implemented in SAS for service results, stillbirths and calving ease.

The results showed the existence of polymorphism for both loci studied. Four different band patterns in IL-2 and seven different band patterns in IL-10 were observed. At the IL-10 locus, striped patterns 5 and 6 had the highest frequency and pattern 3 showed the lower frequency in the individuals with residual values below the mean. In the second group with residual values above the mean, the highest frequency was observed for pattern 6, which also had the highest frequency in the total samples. For IL-2, patterns 1 and 2 showed the greatest and lesser frequency, respectively, in the individuals with residual values below the mean. Pattern 4 had the lower frequency in this locus. Statistical results showed the significant association of IL-2 on open days and length of gestation. In addition, IL-10 had the significant effect on open days.

Taking into account the polymorphisms in the studied regions for the population of Holstein dairy cows and the association of these polymorphisms with reproductive traits, following confirmation of the results using sequencing approach, these regions could be considered in animal breeding programs.