A study by scientists at the Agri-Food and Biosciences Institute (AFBI), along with colleagues at the Agriculture and Horticulture Development Board (AHDB), has again highlighted the clear benefits from calving dairy heifers at two years old.

The researchers analysed almost 7m lactation records from milk recording data provided by Dale Farm, the Cattle Information Service (CIS) and National Milk Records (NMR), with a subset of 2m Holstein cows born after 2000 split on the basis of age at first calving.

The low-level group had an age at first calving between 21 and 24 months, the middle level between 24 and 30 months, and the high level between 30 and 42 months.

Cows in the low level produced an average of 30,901kg milk (energy corrected) in their lifetime which is 1,137kg and 3,570kg (13%) more than the average of the middle and high-level categories. In NI, the study found that average age at first calving was 28.5 months.

Rearing cost

As well as reduced lifetime performance, the researchers also point to previous work which showed that increasing the average age at first calving in a 100-cow herd from 25 to 28 months increases the rearing cost by 18%. Across the entire herd it is extra expense of around £5,800/year.


The age at first calving is driven by management and genetics. The AFBI / AHDB study found that cattle with higher profitable lifetime index (£PLI) have reduced age at first calving. For every £10 increase in £PLI, age at first calving is reduced by three days.

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