For the sixth year in a row, the same purebred shorthorn cow on Steve Parson’s Gingin farm has surprised her owner with twins.
Affectionately known as Zena, the experienced matriarch has needed no assistance with the births, and the resulting progeny have all grown out to full size.
Twins in cattle are often a blight on the farmer, producing more headaches than beef.
The problems begin with birthing, with twice the chance of malpresentation and exhaustion inhibiting natural birth. Conversely, the lower
birthweight of twins can make birth easier. With twins often born up to two weeks early, some farmers can also be taken by surprise.
However, like her warrior namesake, Zena has breezed through, and has produced double the weight of beef in the past 6 years compared to her
single bearing herd members. So with twice the production for half the trouble, not to mention the feed – why don’t we increase multiple births on the farm?
The occurrence of twinning is largely attributed to chance and genetic predisposition, with the chances with a twin birth occurring in cattle, between 1 and 7 %. A US study in 1975 showed the likelyhood of twins was different between breed, with dairy cattle experiencing a higher frequency. Dairy cattle ranged from a 1.3% incidence in Jerseys, 3.4% in Holsteins and an 8.9% incidence in Brown Swiss. Small differences were reported in beef breeds with Hereford cattle having the
lowest incidence (0.4% or one out of every 250 births) of twinning while Angus had 1.1% incidence.
The Bos Indicus breeds experienced 0.2% and 0.4% twinning rates.in Brahman and Santa Gertrudis, respectively.
Apart from breed and genetics, female fertility is also affected by nutrition, management and disease, with nutritional health being of prime importance to
conception rate and ability to bring a healthy calf to term.
Steven maintains that at least in part, Zena’s amazing fertility can be attributed to good feed, and his carefully managed 118 acres are producing more than
enough feed for his small herd of 30 without extra grain or hay required. He also attributes the health of his animals to the high mineral content of his soil.
Until this year all of Zena’s calves have been heifers, however this year, she’s produced both a heifer and bull calf, which means the young heifer has a greater than 90% chance of being a ‘freemartin’ – or infertile female. This phenomena is the normal outcome of mixed-sexed twins in cattle, although has been
recorded in other mammals such as sheep, goats and pigs.
The science is explained as such; during pregnancy, the male fetus begins producing hormones before the female fetus. This extra testosterone shared by
the male fetus via the placenta, adversely affects the female at a critical point of reproductive development. The result is a masculinised female – who is infertile and often exhibits masculinized behavior. Twins of the same sex generally have no problems, and the male twin of a freemartin is also unaffected.
In beef cattle production, an infertile heifer still has value, especially as the freemartin cow can muscle up like a steer, however in dairy production
(where ironically there’s more chance of twins) it’s all about the production of females, so the occurrence of twins wouldn’t be worth encouraging.
However, for Steve Parsons, it’s two for the price of one, and he couldn’t be happier with his lucky twinning cow.