Distribution of sexes within the left and right uterine horns of cattle

Abstract

In cattle, limited data are available regarding the sex ratio of the offspring in relation to the horn of gestation. Therefore, the objective of this study was to evaluate the sex ratio of fetuses gestated in the left and right uterine horns of cattle ( Bos taurus, Bos indicus and crosses). The distribution of male and female fetuses in the left and right uterine horn was analyzed on gravid, abattoir-derived reproductive tracts and artificially inseminated crossbred cows. The total number of fetuses/calves and the sex of the fetuses/calves gestated in each uterine horn were used as the end point for side comparisons using the Glimmix Procedure. Of 64 gravid reproductive tracts evaluated, 29 (45.3%) pregnancies occurred in the left uterine horn, whereas 35 (54.7%) occurred in the right. The sex ratio (% males) of fetuses in the left uterine horn (37.9%) was significantly lower than the sex ratio detected in the right uterine horn (65.7%). Of 113 pregnancies evaluated in artificially inseminated heifers, 53 (46.9%) occurred in the left uterine horn, whereas 60 (53.1%) occurred in the right uterine horn. The sex ratio of calves gestated in the left uterine horn (35.8%) was significantly lower than the sex ratio of calves gestated in the right uterine horn (63.3%). In conclusion, in these experiments, a significantly greater proportion of males were gestated in the right uterine horn of cattle and a greater proportion of females in the left uterine horn. Further investigation is needed to determine the mechanisms underlying the observed disparity of the expected sex ratio within the uterine horns of cattle.