Calving interval has increased
UK dairy cows have an average calving interval seven days longer than three years ago and interval to first service has increased by the same amount, according to NMR data.
This could be evidence of a conscious decision to delay first service in high yielding herds, says NMRs Mike Blanshard. "An increase in lactation value and low calf prices are good reasons for this, but it can lower lifetime yields."
When a cow spends longer in late lactation yielding 10 litres a day, rather than at peak yield – typically 35-40kg – it could reduce output by 3000kg in a four lactation lifetime, he calculates. That milk is worth £570 at 19p/litre.
Cheshire vet Neil Howie, of the Nantwich Vet Group, believes some herds are delaying first service in high yielders until they have a good heat. "Some cows are not ready to get pregnant and vets are more inclined to suggest waiting a month for cows to gain condition rather than treating with hormones.
"But there are herds in which high yielders calve within the national average of about 400 days."
Mr Howie is concerned that the falling national fertility level provides some producers with an excuse for lax management. "There is probably a genetic component to poorer fertility and higher yielders are proving more difficult to feed. But you can fight it, by managing cows for the whole lactation and during the dry period to maintain body condition and intakes." *