Male fertility is negatively affected by female hormones. The size of the testes and production of sperm is reduced in males supplementing with female hormones, reports TransGenderCare. In addition, the size of the penis and prostate reduce, sexual drive and frequency of erections drops, and the volume of ejaculate decreases.
When males supplement with female hormones, marked changes occur to the reproductive system. Most noticeable is the reduction in the size of the testes, while the penis does not exhibit as drastic of a change, according to TransGenderCare. The production of sperm and testosterone drop accordingly, negatively affecting ejaculate quality and sex drive. In addition to reduced sperm count, the volume of ejaculate lessens. Thus not only does the male ejaculate low quality semen, but less of it as well.
A 1997 study by the University of Illinois Urbana-Champaign illustrates the mechanism behind this phenomenon. The researchers examined the regulatory role of estrogen in the release of sperm from the testes into the efferent ducts. Estrogen was actually found to be necessary to produce high quality sperm, as it promotes the re-absorption of non-essential fluid from semen and thus produces high concentrations of sperm. While the researchers admit estrogen is required for healthy ejaculate, an overstimulation of these receptors in the male reproductive system have deleterious effects on fertility.