Did you know that a heifer (female) calf that is twin to a bull is almost certainly infertile?  Apparently bovines are the only animals that this happens with – goats and sheep can have multiple births and all will be fertile.

Medley of Yearling Heifers

The reason is that the testosterone in the womb from the male renders the female calf infertile.  That’s partly why twin heifer calves are such a bonus in a dairy herd as not only are both fertile but dairy heifer calves are worth more than bulls. We had one twin heifer a couple of years ago that was seen bulling (on heat) and subsequently went in calf and is still in the herd. This may have happened as her reproductive system developed when the levels of testosterone were low.

Bringing In The Cows


We have 3 probable ‘freemartin’ yearling heifers this year. Brian had noticed one showing signs of being on heat so when the AI technician was inseminating other heifers, he got him to check her the other day.  He could feel one ovary (through the rectum) but she doesn’t have a cervix or vagina. So she has some reproductive organs but not all of them – the presence of the ovary caused her to display some signs of being on heat but there’s no way to get her pregnant. What happens to these infertile calves?  Freemartin heifers are fattened at 2 years of age and sent to the factory.

Do twins stay close throughout their lives?

We have had sets of twin heifers that seem to recognise their relationship all through life. One set of twins were separated as yearlings for a while into 2 different batches and yet, when reunited, continued to always graze close by each other and come into the milking parlour in the same row. I’ve noticed twin calves lying close to each other in the pens too. It just shows blood is thicker than water :)

8 thoughts on “Bovine Twins – Why a Heifer Twin Can Be Infertile

  1. Lorna, it is interesting that you’ve noticed this ‘closeness’. We’ve had a bit of an issue separating a family of pigs this week…. brothers and sisters just kept breaking out to be with each other! As you say blood is thicker than water!

  2. Very interesting that they seem to stay close. Also very interesting about the heifer that had an ovary but nothing else – nature is bizarre! I learnt about freemartins when I was doing a short work experience placement at a dairy farm (but didn’t learn any more than that they exist). Do you know why they are called freemartins? I always thought it was a bit of an unusual name.

    • It is an unusual name, no idea where it came from.
      Nature is strange alright. We had triplets for the first time ever last year – two bulls and one heifer. The heifer died from Rotavirus (we lost 3 calves) and we were all really upset – partly cos she was unusual as she was partly Belgian blue and partly cos she was special as a triplet – even though she wouldn’t have ended up in the dairy herd as she’d almost certainly have been infertile.

  3. Good Blog, I’m quite often asked about why we don’t keep the heifer from a bull/heifer twin.Non farmers find this very strange!! Here in NZ, we put them on the truck at 4 days old.

    • Do you slaughter bulls that young too? Putting them on the truck means slaughtering I guess? Here, we fatten them and they usually go to the factory at 22 months of age.
      We’ve had one or two that ended up being fertile but it is rare

  4. Great blog Lorna, I didn’t know about Freemartin heifers! Did I ever tell you I did my PhD on the gene expression of the bovine (dairy) mammary gland? The idea was to see if a particular milk secreted protein would be expressed at oestrus and therefore act as an easy marker. I did find one potential protein and I do know another lab took it on to see if could be advanced. The ultimate goal would be to have a milk-based dipstcik test that would accurately indicate oestrus in dairy cattle!

    I like the idea that the twins tend to recognise their bond, sometimes we underestimate animals and their connections and sensitivities!

    • I didn’t know that Naomi, gosh, something like that would be worth a lot of money – anything to make it easier for farmers to detect cows in heat and ensure they get served. Some farmers are brilliant at detecting them, some aren’t so good. My husband is great, I’m useless! ;)

      Like humans, some animals are more intelligent than others and yep, I do think some animals are more intelligent than some humans :)

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