Twins in cattle can create challenges. One of them is the arrival of a freemartin, an infertile female that can result when one twin is male and the other female.
Dr. Colin Palmer, associate director of the University of Saskatchewan Livestock and Forage Centre of Excellence, says 85 to 90 percent of female calves born as co-twins to bull calves are freemartins. It can also happen in triplets.
Freemartins are most common in cattle, says Palmer, but “this also occurs in sheep and goats, but only about six percent of co-twins in sheep and goats are freemartins.”
The freemartin heifer is a result of shared exposure of hormones in the uterus. “This occurs early in the pregnancy, around 30 days of gestation. At that time the two placentas that surround and support the male and female calf can become closely connected or fused, allowing exchange of cells and hormones,” says Palmer.
“The fusion of placentas and sharing of blood allows some exchange of cells and hormones and there can be variability in how the sex organs develop. Development of the male reproductive system tends to dominate during early development.
“Along with testosterone, the male chromosome (XY) also becomes present in the female calf (XX), causing development of a freemartin heifer with a mixed XX/XY chromosome, also known as a chimera.”
The mix of male and female chromosomes makes freemartins appear less feminine. Past weaning age, they generally look more masculine and more like a young bull or steer.
“These heifers sometimes have masculine behavior and are more likely to mount other cattle. They don’t have a penis, and can’t breed, but their tiny ovaries may contain what looks like testicular tissue,” says Palmer.
Freemartins produce more male hormones than normal heifers and the extra testosterone leads to bullish behavior. The reproductive tract is abnormal, even externally.
“There is generally shorter distance between anus and vulva. In a normal yearling heifer there’s usually about three inches between the top of the vulva and the anus. In a freemartin these are closer together. The vulva is tiny and the bottom is often tipped up, with a large tuft of hair at that location,” says Palmer.
“We used to have a lot of twins in our own herd and some of the heifers were freemartins. We had one that was easy to tell from the time she was a young calf; she had a funny-looking vulva. The urethra was exposed to the outside, and when she urinated, she could spray urine 10 feet. The kids noticed this right away because that heifer could hit you with urine if you were behind her.”
Most cattle producers don’t keep a heifer if they know it is a co-twin but there are cases when they aren’t certain.
“Sometimes I find freemartins while preg checking heifers. They don’t have a normal reproductive tract. Often it’s very tiny and undeveloped,” Palmer says.
“When I discover a freemartin and ask if she was a co-twin, usually the producer is certain she was not. But it could be a situation where one of twin embryos is lost early on and the pregnancy continues with just one fetus.
“Even if you were there at the birth of a female calf, with no bull calf born with her, there might have been exposure to a bull calf embryo in the uterus early in gestation.”
In other instances, twins might not be observed at birth and one might die with no one realizing the survivor is a freemartin.
Identification of freemartins used to be done by palpation or by probing the vagina once the heifer was older. Today a DNA test can tell the tale.
“The freemartin is a type of chimera, which means she has both XX (female chromosome makeup) as well as XY chromosomes in her blood and gonadal cells. Chimeric conditions vary. Not every cell type in the body will express this genotype.
“ If you contact a lab that does DNA testing and want them to check if a heifer is a freemartin, the lab will likely ask for a whole-blood sample,” says Palmer. A hair sample may be inadequate.
If it’s a nice heifer, especially a purebred, the owner might want to see if it is normal.
“Up to 15 percent of co-twin heifers are normal and there is no reason not to keep them as cows,” Palmer says.