With better nutrition and management and a higher incidence of twins in the exotic and Holstein breeds some larger herds can have up to a 10 per cent twinning rate. With the odds of 50 per cent of the twins being mixed sexes it is no wonder freemartins are not an uncommon occurrence. Remember though that being twins of mixed sex does not guarantee the female will have none or undeveloped reproductive organs. In eight per cent of the cases a normal intact heifer is the result which if kept could reproduce normally.
Freemartins become a bit of a management headache for several reasons. They are often the ones orphaned on to another cow and their identity as a twin may be lost. Because of their masculine characteristics they grow very well and most often end up in the upper 25 percentile for growth so inadvertently will be kept as replacements.
If in the feedlot, and identified, they should be given a steer implant as their hormonal profile more closely mimics a steer. The issue here is they tend to get ridden lots if put in the steer pen and are the more aggressive ones if put in the heifer pen. Sometimes they end up in the chronic pen and stay there until finished.
Veterinarians can pick out these freemartin heifers if you have them palpated to select for breeding soundness. Several beneficial things are accomplished at palpating. As mentioned the freemartin heifers are identified and removed along with any pregnant ones and those with abnormally small pelvises or reproductively underdeveloped. One must remember, intact twin heifers will be genetically predisposed to twin themselves. If you want a higher incidence of twins in your herd select them as replacements. If not, cull them out. The choice is yours.
If you don’t palpate heifers before selection the management issue is to keep track of these freemartin heifers. The first is identifying them for sure. There are several ways to do this. Most have abnormally developed external genitalia with a very prominent protruding clitoris and what I describe as feathery vulval lips. There is a small instrument that measures the depth of the vaginal vault or you can use a plastic test tube. Measure some normal heifers to get the average depth. Freemartin heifers will be considerably shorter to the point of having no vaginal vault.
This measurement should be taken within a few days of birth. Then identify the freemartins with a distinct tag or notch their existing tag. The bottom line is making them distinguishable down the production line. Blood or DNA tests can also be done for freemartin determination and is useful if their external genitalia look normal and they are potentially valuable breeding stock.
The huge loss with freemartins occur when they are kept, and kept, and kept, but never have a calf while remaining in the herd. I have personally palpated several four-to five-year-old freemartins when the producer wondered why they had not calved. If you purchase heifer replacements, keep in mind some will be freemartins. When palpating show heifers in pen-of-10 or pen-of-five competitions it is not uncommon to find some freemartins. They are selected because they have superior growth.
A good rule when selecting heifers is to always remove the top five per cent for growth as they may have higher levels of male hormones and similar to freemartins will have poor fertility or be totally sterile.
If you see dairy heifers for sale, do an about-face, as they most likely are freemartins. Most intact dairy heifers are kept as replacements with the high culling rate in the dairy industry.
I once was spaying heifers at a feedlot and spent some time trying to spay a freemartin before finally realizing it. Only later did I discover the producer had written “twin” on her tag. Had we been paying attention the procedure would not have been necessary.
It would be nice to have a standardized method of marking freemartins across the industry, but that will never come to pass. I have looked at some triplets and the same principal applies. Most are freemartins if there is a bull calf in the mix. I wonder if other similar species such as bison, yak or water buffalo have the same issue when twins arise. Although twins are much rarer in bison for sure.
We rarely see hermaphrodites (intersexes) in the cattle industry but these should be put in the same category as freemartins. They are sterile and should be fed out as slaughter animals. The beef from all these animals is high quality. Their genetic condition has no bearing on the taste or tenderness of the meat. In fact, they make good freezer beef for the owner.