Twin mysteries: what we know (and don’t)

Sisters . . . The Ayshire twin cows on Cameron and Marion McFadzien’s dairy farm are never far apart. PHOTO: HENRY MCFADZIEN

A set of Ayrshire twins have been a source of interest since they were born four years ago at Achamohr Dairies.

My son, Cameron, and his wife, Marion’s, Achamor herds are predominantly Friesian with a few Kiwi Cross, and, to experiment with an outside cross, a few cows are inseminated with Ayrshire semen.

As a result, two inseparable identical twin heifer calves were born, and we have been fascinated by them ever since.

I mentioned them in a column several years ago when they were first calvers and how they do everything in tandem.

They had their calves only a day apart, they come on to the rotary milking platform with only a few bails between them, graze within a short distance out in the paddock and, as the photograph suggests, can’t do without each other’s company.

Why do they have such a strong bond? Is it telepathic?

I’m sure we have all heard anecdotal stories of human identical twins claiming something mysterious, a special psychic connection.

However, scientists tend to play down telepathy as coincidences.

Is it because they are Ayrshires in a Friesian herd and there is separatism between the breeds?

If so, are they at the top or bottom of the pecking order?

When the cows come in for milking the same ones are always first and the same ones last, according to where they are in the pecking order.

With sheep, many years ago, my father put a Lincoln ram and six Southdown rams out with 500 ewes.

The Lincoln got more than his quota as he left 180 lambs.

There were always ewes hanging around him as if he was No1 preference.

In the natural animal world like goes to like.

For example, birds of the same species flock together.

Did the ewes still have that instinct going for the same phenotype?

The Ruakura Research Centre used to buy identical twin heifer calves off farmers around the North Island to experiment with and were able to gauge the effects by using the same genetics on experiments with relatively few animals and the results were more precise.

A cow that has twins usually keeps on having twins.

Identical twins happen when one egg is fertilized by one sperm and are either bulls or heifers, whereas fraternal twins happen when two different eggs are fertilised by two sperms.

The majority of twins are fraternal.

Half the time the fraternal twins are both either bull calves or heifers.

Where the twins are a bull and heifer, 90% of the heifers are freemartins and, being infertile, won’t breed.

The male is not affected.

I don’t know of another species where that happens.