Influence of the semen deposition site on the calves' sex ratio in Simmental dairy cattle.

It has been suggested that the time of insemination has effect on the calves' sex ratio because of the differences in timing of capacitation, motility and survival time of the X and Y spermatozoa in the female reproductive tract. We have conducted a field trial to study the effects of different semen deposition sites on the sex ratio and fertility in cattle. Two groups of 450 cows were inseminated via artificial insemination: group A was inseminated into the uterine body and group B was inseminated deep into the uterine horn ipsilateral to the ovary with dominant follicle. After applying several exclusion criteria, a total of 607 pregnant cows were considered for data analysis (group A = 318 and group B = 289 cows). The conception rate was 7% higher (p < 0.05) in the group A, with 23% more of the male calf pregnancies (p < 0.001). At the same time, 18% more of the female calves were calved in the group B (p < 0.005). The difference in male calves between the two groups was 21% and in female calves was 20% (p < 0.001). We conclude that semen deposition site plays a significant role in differences in gender ratio observed after calving. Intracornual semen deposition resulted in a higher ratio of female calves, whereas uterine body deposition site resulted in higher male calves ratio, probably contributing physiologically to the differences in motility, capacitation time, the lifespan of X vs Y spermatozoa and to the pronounced shift of X spermatozoa in the female genital tract.