Question: I had a set of twins born, one a heifer, the other a bull. My understanding is that at least 90% of heifers born twin to a bull will be sterile. This is a registered calf and I would really like to know if she is fertile. Is there a lab test for freemartins?
Answer: I have read that statistic too, and I'm still looking for the 10% that are supposed to be fertile. I'm sure they are out there somewhere.
For those who do not know, a freemartin is a female born twin to a bull that has a very small, underdeveloped reproductive tract. In cattle, twins almost always share the placental circulation. As a result, the developing female fetus is exposed to male hormones from the bull. This suppresses normal development of the female reproductive tract. As the heifer develops, the vulva is often obviously small. If the heifer is large enough, rectal palpation will reveal a small, underdeveloped, rudimentary reproductive tract.
Early detection can be very important in deciding how the heifer should be handled and developed. The "pencil test" can be used to screen these heifers, where a lubricated test tube or the eraser end of a No. 2 pencil is inserted into the vagina. If the test tube or pencil cannot be inserted more than 7 cm (about 3 inches), the heifer is a freemartin, and no further testing is warranted. Passing this screening does not, however, mean the heifer is normal. Lab testing will still be warranted if you want to keep her.
Several labs offer blood tests that are very accurate when it comes to determining this condition. Your veterinarian can give you more information on testing and advise you on how to proceed.
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