Freemartinism is a severe form of sexual abnormality in cattle. Affects female calves born to male twins 90% of the time and results in infertility.
Male calves are rarely affected, however, there could be a little reduction in the size of the testicles. Larger testicles in bulls are associated with high levels of fertility.
After conception, the twin calves developed at different rates, especially when they are male and female. The male reproductive system develop earlier than the female reproductive system.
Since both the male and the female share the plancental membrane, this means that they (the twins) share the placental fluids. This sharing leads to mixing of blood, hormones and antigens responsible for sex differentiation.
The chief hormone is the Anti-Müllerian hormone (AMH), also known as Müllerian-inhibiting hormone (MIH). This hormone is produced by the sertoli cells in the testicles of the male and it inhibits the development of female reproductive system.
As a result, the shared blood carries these hormones and exert its effect in the female twin leading to poor development of the female reproductive tract. The ovaries are underdeveloped and are incapable of producing eggs. The vaginal tract may also be shorter than in a fertile heifer. The uterus is also severely underdeveloped rendering it incapable of producing sufficient hormones to maintain a pregnancy.
Freemartinism is not a genetic disorder. It is a random occurrence that happen to affect female calves born with male twins due to the circumstances that we have discussed above.
The females cannot pass the trait to their offspring because they are incapable of carrying a pregnancy. Usually, a freemartin is used for research (stem cell development) or fattened for slaughter.
Freemartinism is very characteristic. Freemartins exhibit underdeveloped reproductive organs. They may have enlarged clitoris, shorter vaginal tract, a smaller vulva with a tuft of hair and deformed udder. They also have an underdeveloped uterus incapable of sustaining a pregnancy.
In some cases, the features may not be very evident, especially if the male twin was aborted in early pregnancy. Under these circumstances, a blood test may be necessary to determine the male (Y) chromosomes in the blood.
Freemartinism occurs randomly in female calves born to twin males. No external intervention can prevent it from happening.
This is a subject that still needs a lot of studies. We are open to research findings that will intervene on freemartinism.
A dairy farmer does not benefit from a freemartin heifer. The sooner you can identify and eliminate it the better for you.
The freemartin heifer cannot be bred and it cannot produce milk. Keeping it at the farm will only drive up your production costs.