The effects of altering the pH of seminal fluid on the sex ratio of rabbit offspring.

It has been suggested that the pH of the vagina at the time of fertilization may have a differential effect on X- or Y-bearing sperm and thereby affect the sex of the offspring. To test this postulate, rabbit semen was collected, diluted 1:10 with a buffer of pH 5.4, 6.9, or 9.6, and after 20 minutes 0.5 ml of semen-buffer mixture was used for insemination in an ovulation-induced female. Newborn pups were examined both externally and internally for gender. The females inseminated with acidic semen had 6 litters, 50 offspring, with 48% males; those with neutral semen had 8 litters, 48 offspring, with 63% males; and those with alkaline semen had 7 litters, 49 offspring, with 49% males. There was no significant difference in these sex ratios from the expected 50% males. Motility of rabbit sperm at 23 degrees C in buffers of pH 4.6, 5.4, 6.9, 9.6, and 9.8 was reduced in vitro as the pH deviated from neutrality. Acid conditions were more detrimental than alkaline conditions. Sperm lost their motility more quickly in buffers of 37 degrees C than in buffers of 23 degrees C. It was not possible with scanning electron microscopy to distinguish morphologically between X- and Y-bearing sperm. It seems unlikely that a direct effect of pH on sperm can be a single influence on the sex of offspring.