7 December 2001


By Robert Davies

Wales correspondent

THE causes of declining dairy cow fertility may be complex, but herd managers must take some basic steps to prevent the current 40% pregnancy rate dropping to zero by 2040.

Glos dairy vet Roger Blowey told producers attending an MDC Fertility in Focus roadshow in Wales that he had no magical solution to halt the 1%/year fall in conception rates in high yielding herds.

However, solutions must be found to cushion the impact of economic pressures on herd management.

Producers are being pushed into chasing ever-higher yields from bigger herds.

Genetics are improving and nutrition modified to allow cows to express their enhanced yield potential, said Mr Blowey of the Wood Vet Group.

Cows now spend more time spent standing on concrete for feeding and milking, and stockmen have to monitor larger herds. All these factors contribute to poor and inaccurate heat detection, irregular oestrus, hormonal imbalances and embryo rejection.

"A stressed cow can get so many extraneous hormone signals that she may not recognise the presence of an embryo and it is expelled when prostaglandin is released," he explained.

"Heat detection can be a real pain as herds size increases. But when only 50% of heats are detected in a 100-cow herd and there is a 50% conception rate only 25 cows will be pregnant after three weeks of the service period."

Most cows come on heat between 10pm and 5am with 20% of cows staying on for less than six hours, so the chances of catching them could be slim. Trials show that one-fifth of cows are mounted less than six times and there is an average of 20 minutes between mounts.

It is, therefore, far from easy for a busy stockman to spot a bulling cow in time to get her inseminated during the six to eight hours an egg remained viable after ovulation, he added. Other cows which were about to come on heat themselves were the best indicators of oestrus, so synchronisation could help.

Detection errors are also fewer when housed cows are provided extra space such as loafing areas, are not lame and are confident about being able to keep on their feet. He advised that low level lighting should be kept on all night to help the person carrying out heat checks, which should be done when cows are resting and not feeding.

"It does not matter what housing looks like as long as it is comfortable. Calving and early lactation are major stresses at the time we are trying to get cows back in calf."

He was particularly concerned about the way heifers were integrated into the herd. In a short time they could face the stresses of calving, a sudden change to a high-octane diet, their first introduction to adult cows, a move onto concrete and life in cubicles.

It was astonishing that some producers dont cubicle train heifers or use transition feeding, added Mr Blowey. However, an alternative solution is operating a separate milking heifer group.

At calving, the immune system is also suppressed to avoid the hypersensitivity reaction that can result from the possible mixing of foetal and dam blood. Trials show that where a heifer or cow became sick the average gap between calving and conception was 80 days longer than for a fit animal.

Whether dealing with heifers or cows, herd fertility is influenced by a series of events between one calving and the next. Improving the fertility of cows on any one farm depended on recognising and putting right the initial causes of unsatisfactory results, he said.

"Look at your own systems and see where management could be better. I cannot supply you with one answer to the problem of poor fertility. It is easy to blame the Holstein, but genetic improvement is just one factor."

He added that while economic pressures would continue to dictate fertility influencing management decisions, milk producers could mitigate against some effects by getting the basics right. This included nutrition, cow comfort, general cow health and accurate heat detection.

Cows with conditions such as acidosis a uterine infection, sore feet, or afraid of being bullied or slipping on wet concrete, are much less likely to become pregnant, he pointed out. &#42


&#8226 National decline concern.

&#8226 Herd management can help.

&#8226 Identify problems on farm.

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