September and October are crucial times of the year for heifer rearing on dairy farms. You should now determine if your heifers are achieving their target weights.

Yearling heifers should be 35% of their mature body weight, while in-calf heifers should be 75%.

Your heifer’s mature body weight should be determined by the cows within your herd, not on estimated figures based on breed.

To determine what is the mature weight of the cows within your herd, select a sample of ten cows. They should be a fair representation of the cows within your herd and a mix of different ages.

If you determine that the average weight of cows within your herd is 580kg, your in-calf heifers should be 435kg and your yearling heifers should be 203kg.

Target weights

Heifers failing to reach target weights will have a negative impact on their fertility and production going forward.

If you determine that a number of heifers within your replacements are behind target by 5% (413kg in-calf heifers and 193kg for yearling heifers) or more, you need to act now.

These heifers should be offered priority grass and/or concentrates if required. You need to ensure they are the correct weight by calving and turnout.

Yearling heifers

Puberty in heifers occurs once they have reached 42-47% of their mature cow weight – failure to reach targets will result in heifers not meeting breeding targets.

So it is important that your yearling heifers are reaching their target or you may have a number of empty heifers come scanning.

A heifer calving at 24 months-of-age has a rearing cost of €1,500. This means the cost of rearing heifers is not returned until midway through her second lactation.

So ensuring that these heifers reach their targets and go in-calf is important.

In-calf heifers

If your in-calf heifers are behind their target it is also important that they ‘catch up’ before calving.

Calving a heifer below the ideal target weight may lead to an increase in calving issues. As previously mentioned, rearing a heifer has a cost of €1,500, losing a heifer during or shortly after calving means these costs are not recuperated.

Heifers calving behind their target weight will have a lower milk production in first lactation, and it may also impact on their lifetime production.