29 December 1995

Reduced intake leads to a jump in empty cows

Scanning dairy cows at ADAS Bridgets has found more than the usual number empty. Jessica Buss reports on a problem that may be affecting other herds, too

ADAS Bridgets Elite herd has maintained a tight calving pattern and achieved very good fertility results until this summer. Suddenly, more than usual were found empty at scanning.

Although high yielding cows are often considered more difficult to get in calf, the fertility of Bridgets Elite cows producing more than 12,000 litres a cow has until now been satisfactory, according to centre manager Dr Bridget Drew.

Royal Vet College resident vet Paddy Gordon claims this years poor fertility results are due to heat stress resulting in reduced dry matter intakes.

Heat stress is also known to cause embryo death, particularly when cows are dry.

"During the dry period the follicles in the cows ovaries start to develop," he says.

"This is two to three months before the cows are served and when the egg released at bulling in the service period starts to develop. Nutrition of the cow at this time is crucial for conception rates, as the viability of the resulting egg can be reduced."

Mr Gordon says that another reason for poor conception rates could be reduced intakes in the build-up to peak lactation. "For weight loss can result in low progesterone levels, delayed ovulation or reduced interaction between hormones," he says.

Late summer calvers

Dr Drew cites figures from ADAS Datamate fertility recording service which show that late summer calvers are the most difficult to get in calf. "One of the problems during this period is the change of diet during the breeding season," she says.

"Cows are also less easy to see bulling at grass, especially late at night, so they do not get inseminated soon enough."