Why twining occur in dairy cows, advantages and danger

Twinning is especially a good thing for animals that are traditionally uniparous. Twining is a factor of genetics but hormonal treatment can trigger it. Similarly, it can happen when reproduction technology is used like Embryo Transfer.

Through these reproductive technologies, animals are induced to release more than one egg which are either fertilised internally inside the animal (in vivo) or outside the animal in labs (in vitro). In cows though twinning is uncommon, in dairy breeds it does occur in their second calving. Twins can either be identical (monozygotic from one egg) or can result from two different eggs – fraternal (dizygotic).

The benefits

Advantages of twining include a higher number of calves or reproduction by the dam. Cows that have twinning have been found to produce more milk compared to those that have single birth.

But are there any disadvantages associated with twinning in cows? Yes. Research has shown a number of challenges that come with twinning in cows. Twin feotuses present a delicate development process as they share the blood supply in the womb.

The dangers

If the twins are of a different sex – male and female – up to 50 per cent result in Freemartins where the female calve picks male characteristics and will be infertile. That aside feotal deaths and abortions are common with twin pregnancies in cows.

Difficult birth and retained afterbirth is a common problem with dams carrying twin pregnancies. Calf abandonment is relatively higher in cows that have twins and subsequent calf mortalities. Weight at weaning is also low for twins which predisposes most twin calves to early mortalities. The dam will take a bit longer to get back to cycle increasing the inter-calving length.

Even if genetic selection for twining was done; it has shown to have low heritability score and low repeatability. Therefore, embryo transfer is the only means of quickly utilising the good genetics of a superior cow. Look out for a comprehensive article on embryo transfer in future.