| An asymmetric distribution of the sexes within the left and right uterine horns has been described in multiple polytocous, laboratory species. A series of experiments were conducted to evaluate the sex ratio (% male) of calves gestated in the left and right uterine horns, as well as the sex ratio of embryos originating from the left and right ovaries of cattle. In Experiment 1, the sex ratio of calves and fetuses gestated in the left and right uterine horns was investigated. The sex ratio of calves and fetuses gestated in the right uterine horn was significantly higher compared with the sex ratio of calves and fetuses gestated in the left uterine horn. In addition, the sex ratio of the left and right uterine horns differed significantly from parity. In Experiment 2, embryo transfer data were analyzed in an effort to determine if sex-specific selection pressures were applied to embryos in the uterine horn of transfer. The sex ratio of ET calves born following transfer to the left and right uterine horns was not significantly different. Similarly, the overall sex ratio of calves born in this experiment did not differ significantly from parity. The sex ratio of embryos recovered from the left and right uterine horns of superovulated beef cows was evaluated in Experiment 3. The proportion of male embryos collected from the right uterine horns was significantly greater than from the left uterine horns. The sex ratio of embryos recovered from the uterine horns in this experiment was not different from parity. In an effort to determine the role of interovarian communications in the sex selection process, the sex ratio of embryos recovered from unilaterally ovariectomized superovulated beef heifers was investigated in Experiment 4. The sex ratios of embryos recovered from left- and right-ovary intact heifers were not significantly different. In Experiment 5, the sex ratio of IVP embryos was evaluated. The sex ratio of the IVP embryos was significantly lower than parity and was not different between ovary of origin. In addition, length of time in maturation was determined not to influence the sex ratio. |
