15 September 1995


Recent research has confirmed suspicions that leptospirosis infection does reduce fertility in dairy cows. Jessica Buss reports

LEPTOSPIROSIS infection reduces the fertility performance of dairy cows. This has been proven in University of Liverpool Vet School studies.

The research confirms that vaccination of herds suffering from the disease will improve breeding efficiency.

Liverpool Universitys Dr Richard Murray claims the study substantiates increasing evidence from farmers and vets that has suggested leptospirosis can reduce fertility.

The University of Liverpool study involved 12 selected commercial dairy herds comprising 1500 cows and the equivalent of 55 years breeding records. These herds had good fertility and health records, adequate nutritional and mineral status, and acceptable milk quality.

The study found that in the year of leptospirosis diagnosis the risk of poor fertility increased fourfold.

"Less cows conceived in the year of diagnosis compared with other years," says Dr Murray.

In the year of infection first service conception rate, overall conception rate, services a conception and culling rate were reduced.

It was also found that more of the cows with high levels of infection failed to conceive compared with those with lower infection levels. Pregnancy rates differed by 28.5% between the two groups.

Studies of herds vaccinated after leptospirosis diagnosis showed that herd fertility improved on all herds vaccinated within one year.

This improvement could be measured using a score for herd fertility devised by Reading Universitys Dr Dick Esslemont and Somerset – based vet Roger Eddy.

It was mainly the result of a reduced culling rate. Other fertility measurements were not significantly altered by vaccination, and although some herds did show improved conception rates, for example, these varied from herd to herd. "But it was the reduction in culling rate after vaccination that was significant," says Dr Murray.

To check the improved fertility was due to vaccination, half the cows in four herds were vaccinated for two years and the other half of the cows were not vaccinated.

Dr Murray claims a significant difference in the fertility status of the two groups of cows. This time improvements were seen in culling rates, and also conception rates, interval to first service, and services a conception. This occurred without an effect on lactation yield, he says.

According to Dr Murray, timing of vaccination also proved to have an affect on fertility. Conception rates fell to 46% when cattle were vaccinated 10 days pre- or post-service. This compared with conception rates of 58% for unvaccinated cows.

&#8226 Studies were carried out by Dr G Dhaliwal and Dr Richard Murray, assisted by Prof Bill Ellis of Stormont, Belfast, and funded by Mallinckrodt Veterinary and The Association of Commonwealth Universities. &#42