Vet on call: When twins are not a blessing on a farm

The two calves looked the perfect high-quality Friesians. The appearance of the mothers, their good production records and the fact that they had been serviced using high-quality semen would convince a buyer that the heifers were destined to be good producers.

The calves were two months old. They had been born just days apart. One was greyish and white while the other was charcoal black and white.

The colour differences were of no concern as Friesians can have many shades of black.

Njoroge, the farm manager, said he had heard that a female calf that is a twin with a male is often sterile. He wanted the greyish heifer examined as it had been born with a dead brother.

I told Njoroge that in 90-97 percent of cases of bull-heifer twins, the female will be sterile. The condition is called freemartinism and such calves are called freemartins.

It is safe to assume that heifers born as twins with bulls are sterile. Fortunately, there is an easy on-farm method of confirming that. I got to the calves and inspected the vulva.

The dark black heifer had a normal vulva with a bit of hair at the tip. Its hip and thigh area had a feminine appearance and it was not heavily muscled.
The greyish calf had lots of hair on the vulva and its thighs and hip areas were heavily muscled, making it look like a bull. The vulva looked poorly developed. “For sure, you have a freemartin,” I told Njoroge.

The farm manager said he had noticed the excess hair on the grey calf though he had never seen a freemartin. He said the twin appeared to have died before term and stayed in the uterus until the other had grown to term.

The dead foetus had only scanty hair and the legs were deformed. I told Njoroge that the death of the foetus had nothing to do with the other twin’s freemartinism.

Freemartinism commonly occurs in cows that have a tendency to produce twins from separate eggs. These are called fraternal twins and can be of the same or different sexes.

Twins from a split of one egg are called identical and are always of the same sex. It is therefore not feasible for freemartins to develop from identical twins.

Sheep and goats may produce freemartins but that is rare. It is normally seen if the sheep or goat produces
three or more young ones in one birth.

The condition is caused by sharing of blood vessels of the placenta between the twins. As a result, there is mixing of the male and female hormones in the foetuses.

USUALLY TREATED LIKE BULL CALVES

Male hormones override the development of reproductive organs in the female calf. The tuft of hair around the vulva of the freemartin is thought to be the same as that at the prepuce of the male.

Later, the female hormones are able to control the final growth stages but the disruption caused by the male hormones is permanent. The heifer calf therefore appears like a bull.

In addition to the external feminine deformities in the vulva, there is more serious disorganisation of the ill-fated heifer foetus.

In almost all cases, the uterus fails to develop and may only be seen as a strand of connective tissue.

Ovaries may fail to develop or develop with testicular and ovarian tissues, making them non-functional. The oviducts, also called fallopian or egg transport tubes, may develop poorly or be absent.

There is no continuity of the reproductive tract from the vulva to the ovaries as the vagina is mostly absent. This makes the freemartin calf unable to function as a female.

Incidentally, the female hormones do not appear to affect the development of the reproductive organs and function of the bull calves born as twins with heifers.

Twinning in cows is naturally genetic. Under natural circumstances, twinning is mainly identical calves.

A higher incidence of twinning is seen in commercial dairy production, especially due to the use of hormones that encourage the release of more than one egg in a heat.

This situation increases the chances of cows producing freemartin heifers. I attributed Njoroge’s case to the hormones we used to induce heat in cows on the farm.

Since we started using hormones on the farm about four years ago, twinning has increased. This was, however, the first freemartin case.

Six other cows were bred through hormone treatment early this year. We can only hope they will not surprise us with more freemartins.

Freemartinism is diagnosed by the history of bull-heifer twin births. It is confirmed by the tuft of hair on the vulva and increased muscular development of the heifer calf. DNA tests are available but they are not commonly used due to high costs, low availability and the fact that it is almost certain a heifer born with a bull as twins will be sterile.

Freemartins are usually treated like bull calves, depending on the practices of the dairy farm. Njoroge said he would rear the heifer to maturity with the bull calves for learning experience.

I’ll be following this case, hoping to find out the state of disruption of the reproduction system when the freemartin is finally slaughtered.