I was wondering if anyone knows the percentage of <br>heifers that when born with a bull twin are sterile and why this is so. I would appreciate any info.
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I have never seen a fertile heifer from twins.<p><p>: I was wondering if anyone knows the percentage of <br>: heifers that when born with a bull twin are sterile and why this is so. I would appreciate any info.<p>
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90% of heifers born twin to a bull are sterile. This is because if the placentas touch in utero, there is usually (almost always) an exchange of fetal blood, resulting in the female fetus receiving male hormones. All feti will be females in the absence of the male hormone, so the female twin, although genetically female, will respond to the hormones and develop masculine traits. clear enough?<br>V
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I have also read that a freemarten can also result from a single birth. Originally there were twins (in utero), but something caused the bull twin to die (miscarried &/or re-aborbed), but the hormone exchange still occured to cause the living twin heifer to be sterile.<p>
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Male embryos produce MDIH, Mullerian duct inhibiting hormone, which prevents the formation of internal female anatomy as the female is the default sex. The common blood supply shared by male and female calves in the case of twins means that the female is exposed to this hormone as well. The heifer's reproductive tract does not develop completely with "blind" tracts and incomplete canalization. Ovaries cease to grow and do not develop appropriate germ cells. Therefore, the ovaries are incapable of producing estrogen and often produce testosterone in substantial amounts. This explains why freemartin heifers often exhibit "bullish" behaviors.
