Our Organisation Search
Quick Links
Toggle: Topics

Fact vs fiction: the ‘myths’ of calving at 24 months

Contrary to popular belief, calving beef heifers at 24 months of age has no negative implications on subsequent lifetime performance when compared to calving heifers at 36 months.

The age beef heifers calve for the first time is a cause of contention among beef farmers. The argument usually boils down to two sides: those that calve heifers at 24 months and those that calve heifers at 36 months.

Although there are pros and cons for both, calving heifers at 24 months of age is the most profitable option for beef farms. Many of the cons for calving at 24 months are anecdotal, but recent research carried out at Teagasc has teased out the truths among these myths.

The realities of calving at 24 months

First and foremost, calving at 24 months reduces the rearing cost of replacement heifers. Older heifers have a higher rearing cost up to the point of calving, with a higher cost to offset when they are productive. In addition to this, older heifers have a larger environmental footprint, as they have higher methane outputs.

Other benefits of calving at 24 months include reduced labour costs, as there are fewer stock groups to manage. There is also an opportunity cost that comes with calving at 36 months, as the increased stocking rate could be replaced with more suckler cows or finishing stock.

It’s not without hard work, however. Good management and genetics is required to achieve calving at 24 months. Good growth rates in early life is critical to ensure heifers reach their target weight at breeding, which is 15 months of age. Selecting heifers with a high Replacement Index is known to reduce the first calving age, as they reach puberty sooner and are more fertile. Nevertheless, management is also important to ensure they have the opportunity to express their genetic potential.

While genetics and management are improving on herds nationally, the proportion of heifers calving at 24 months has not improved for 10 years. This could be due to beef farmers’ preferences. Heifers may have had the potential to reach puberty and be fertile, but if they are not served, they do not have the opportunity to calve at 24 months of age.

Unpacking the preference for calving at 36 months

If farmers decide not to calve heifers at 24 months, they usually wait until the subsequent calving season, which will result in heifers calving for the first time at 36 months. The reasons for this are usually due to perceived anecdotal consequences of reducing the age of first calving. For example, some believe it will stunt growth, result in difficult calving and reduce overall performance in subsequent years.

However, recent research using data collected through the Department of Agriculture, Food and Marine scheme BEEP, as well as national data available from the Irish Cattle Breeding Federation (ICBF), actually dispels some of these myths.

Calving difficulties were more prominent in heifers that calved at 24 months compared to 36 months (assuming genetic merit for calving difficulty of sire and dam was equal), but overall there was a higher number of calving difficulties in heifers irrespective of the age at first calving, when compared to mature cows. To mitigate this, farmers could use a very easy calving bull to minimise the risk of a calving difficulty. In addition, age at first calving had no effect on the risk of calving difficulties in future lactations.

It is often believed that heifers at 24 months are not mature enough to calve, which will influence subsequent performance. Fertility of heifers in subsequent lactations is a good indicator of a heifer’s ability of coping after calving and being able to cycle again. Heifers that calved at 24 months had a more desirable calving interval in lactation one, compared to heifers that calved at 36 months. As well as this, the age at first calving had no impact on the probability of cows surviving to subsequent lactations.

Doing what is best in the long-term

One performance trait that did tend to be affected by calving at 24 months was weaning weight. Assuming equal genetic merit for beef traits, they weaned lighter calves in early lactations; however, the total amount of weight weaned is more for the cow throughout their lifetime, as they will produce an extra calf over the period, which negates the lighter weaning weight in the early lactations.

Finally, there is anecdotal belief that calving at 24 months will stunt growth. Analysis of the BEEP data showed cows that calved at 24 months were lighter at first lactation, but with each new lactation cycle their weight difference decreased, and by lactation five there was no difference to cows calved at 36 months. This suggests that cows were able to cope with the stress of calving and rearing to continue their growth and reach equal mature weight by the fifth lactation. And having a lighter cow in earlier production years is actually beneficial, as they eat less and have a lower environmental footprint. 

Achieving 24-month calving in beef heifers certainly poses many challenges, but it can be done with the right genetics and good management. This research shows that many of the fears around calving at 24 months are unfounded, and that it is actually beneficial for overall cow productivity. 



Only 23% of beef heifers were calved between 22 and 26 months of age in 2021.



In comparison, 74% of dairy heifers were calved between 22 and 26 months of age in 2021.



This research was funded by the Department of Agriculture, Food and the Marine’s stimulus research grants GREENBREED and MULTIREPRO.