23 October 1998

Home in on heat – advice

Dairy cow fertility was the chief topic at a Milk Development

Council-funded meeting held by Dairy Research and

Consultancy at Reading last week. Jessica Buss reports

FOCUSING on heat detection rate in dairy herds will do more to increase pregnancy rate than trying to improve conception rate.

That was the message from Glos dairy vet Chris Watson, speaking at a Milk Development Council technology transfer meeting run by Dairy Research and Consultancy at Reading University.

Improving heat detection rate – also known as submission rate – by serving a higher % of cows due for service during a 24-day period will improve pregnancy rate more easily than trying to improve conception rate.

For example, he explained that on a farm where submission rate and conception rate are both 40%, it is more difficult to improve conception rate by 10% than to improve submission rate by 20%. Few producers achieve conception rates above 50%, but its possible to achieve a submission rate of over 80%.

But most producers are keener to discuss conception rate with their vet and treat cows not bulling or not seen bulling than to monitor and discuss submission rate.

"Heat detection is under-estimated because unlike semen you dont have to pay for it, so awareness of its importance is lower."

To achieve a good submission rate, its crucial to manage cows well in terms of diseases such as whites, and feeding. He advised monitoring body condition score changes before breeding to ensure cows are correctly fed. Observing heats before cows are due for service would also help.

He also believed pre-breeding checks on all cows paid because they identify most whites cases. Checking only cows which have twins, difficult calvings, abortions or post-calving infections will find only half of those in the herd suffering whites, added Mr Watson.

Separate matter

"However, presenting cows for first service and picking up returns to service should be considered separately.

"Many producers are good at detecting heats for first service, but are not as good at detecting returns," he argued.

To improve submission rate to first service, synchronising animals and using fixed time AI on the whole herd can result in a 100% submission rate.

However, pregnancy rates may be reduced. Studies show pregnancy rates after synchronisation of 40-54%, he said. But because conception rates are over-rated this could still be economic in herds where heat detection is poor.

In practice, synchronisation could be used routinely on cows not seen bulling within 60 days of calving, he added.

To detect repeats, he believed milk progesterone testing could help many producers; taking samples on the service day, then 19 and 24 days after service.

The sample taken on service day would show that the cow should be served. After 19 days, 80% of the cows that were going to return would be identified and could be observed for heat. Then, on day 24 the test would accurately predict pregnancy or non-pregnancy.

Pedometers, tail-paint and Kamars could also help improve submission rates, he added.

Conception rates are still important, said Mr Watson. On one farm which had poor conception rates he found that a thermometer, used when thawing straws for AI, was inaccurate and semen was being cooked before use.

"In the longer term the effect genetics have on fertility should be researched. We should be asking whether a bulls semen is fertile and will produce a good conception rate. In the longer term, we should be using genetic selection to pass on good fertility to a bulls daughters."

HEATOBSERVATION

&#8226 Improvements will pay.

&#8226 Consider synchronising cows.

&#8226 Monitor returns using milk progesterone tests.

&#8226 Use heat detection aids.