Sex Ratio of Bovine Embryos and Calves Originating from the Left and Right Ovaries1

Abstract

An asymmetric distribution of the sexes within the left and right uterine horns has been described in multiple 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. The sex ratio of calves gestated in the right uterine horn of naturally mated cows was significantly higher compared with the sex ratio of calves gestated in the left uterine horn. In addition, the sex ratio of the left and right uterine horns differed significantly from parity. The sex ratio of embryo transfer calves born following transfer to the left and right uterine horns was not significantly different. Additionally, the proportion of male embryos collected from the right uterine horns was significantly greater than from the left uterine horns of superovulated cows. The sex ratio of embryos collected from the left and right uterine horns of unilaterally ovariectomized cows was not significantly different. However, more female than male embryos were produced when left ovary oocytes fertilized in vitro. In conclusion, the results of these experiments demonstrate that a significantly greater proportion of males are gestated in the right uterine horn of cattle and a greater proportion of females in the left. Additionally, the data indicate that sex-specific selection pressure may be applied to embryos by ovarian factors rather than by the uterine environment.

In vivo and in vitro study of the function of the left and right bovine ovaries

“…These results are consistent with those of previous studies in the mouse, Mongolian gerbil [29] and similarly, in cattle [8], reporting a significantly greater proportion of males are gestated in the right uterine horn and a greater proportion of females in the left. Additionally, similar to the embryos collected from superovulated cows, the IVF-derived embryos generated from the left ovary produced a lower percentage of male than female embryos, indicating that sex-specific selection pressure may be applied to embryos by ovarian factors rather than by the uterine environment [8]. Several factors have been reported to influence the sex ratio in cattle, including the level of testosterone in bovine follicular fluid [30,31], timing of insemination [32,33], and the maturational state of the oocyte at the time of insemination [25,33].…”

“…Therefore, embryos recovered from the uterine horns can provide indirect evidence about the ovary ipsilateral to the uterine horn from which the embryos are recovered [8].…”

“…In farm species, Arthur [7] described ovarian activity in the mare and noted a greater proportion of CLs present on the left ovary compared to the right ovary. Furthermore, a number of studies were conducted to evaluate the asymmetric distribution of male and female fetuses between the left and right uterine horns in cattle [8,9], indicating that sexspecific selection pressure may be applied to embryos by ovarian factors rather than by the uterine environment [8].…”

Can mammalian mothers influence the sex of their offspring peri-conceptually?

“…More recently, it was found that bovine embryos and calves originating from the right ovary were more likely to be male, while those from the left ovary were more likely to be female (Hylan et al 2009). At the same time, the highly significant effects on the sex ratio, which were found in naturally bred cattle, were not demonstrated in embryos transplanted after IVF.…”

Sexual dimorphic expression and release of transcription factors in bovine embryos exposed to oxidative stress

“…The sex ratio is believed to be affected by numerous factors either in vivo or in vitro including ovarian factors, maternal diets, and culture conditions (Gutiérrez‐Adán, Granados, Pintado, & La Fuente, ; Hylan et al, ; Iwata, ; Rosenfeld & Roberts, ). Furthermore, male and female embryos are known to being differ in their transcription (Bermejo‐Alvarez, Rizos, Rath, Lonergan, & Gutierrez‐Adan, ), epigenetic profile (Bermejo‐Alvarez, Rizos, Rath, Lonergan, & Gutierrez‐Adan, ), and metabolite consumption (Gómez et al, ), which may be associated with their differential response to environmental insults.…”