A decline in dairy youngstock numbers could constrain milk production capabilities, according to the AHDB.
AHDB Dairy senior analyst Luke Crossman said British Cattle Movement Service (BCMS) data for January 2017 to January 2018 showed a reduction in heifer numbers aged under two years old.
Youngstock numbers aged 12-18 months were down by 17,500 head in January 2018 compared with January 2017, while 18- to 24-month-old animals had fallen by about 11,000 for the same time period.
The decline in youngstock was the main driver behind an overall fall in cattle numbers of about 1.4%.
“The drop in youngstock is due to low milk prices in 2015 which saw farmers switch from dairy heifer semen to inseminations with beef breed genetics in a bid to secure better returns,” said Mr Crossman.
The result, nearly three years later, is a reduction in the number of replacements coming into the herd, he added.
Although improved genetics mean milk production is less dependent on cow numbers than it used to be, the decline could still be a constraining factor if other elements such as feed supplies come under pressure, Mr Crossman said.
AHDB figures also show that for the first time since December 2016, year-on-year overall milk production yield dropped in January 2018, albeit by a modest 0.2%.
The recent BCMS data also showed a reduction in the number of cows aged 48 to 66 months, down 21,000 head on last year.
Most of this drop is a result of fewer 42- to 60-month-old cows six months earlier.
But there has also been a reduction in the retention rate of this age bracket, for the fourth consecutive year.