5 July 2002

NO BENEFITS IN CALLING A HALT TO DRY COW THERAPY

When seeking ways of

trimming costs, dry cow

therapy may seem a

suitable candidate. But

research shows stopping it

could be a false economy.

Marianne Curtis reports

COWS treated with intramammary antibiotics at drying off are four times less likely to be infected with mastitis pathogens at calving than untreated cows and yield 200kg more milk over lactation.

Mindful of increasing concern over antibiotic use, Elizabeth Berry has studied mastitis levels in two herds at the Institute of Animal Health (IAH), Compton, Berks, and in two converting organic herds. Each herd was split with half of animals receiving dry cow therapy and half, not.

"Until about four years ago, dry cow therapy was used on 99% of UK dairy cows, but as some herds have converted to organic and some producers have chosen to be more selective about which cows they treat, this figure has probably fallen to 95%."

Reasons for therapy

Dry cow therapy has three functions, she says. "The first is to prevent summer mastitis, the second is to clear existing infections and the third is to prevent new ones. With low cell count herds, such as those at the institute, the last is the most important."

For the study, 236 IAH cows with an average annual rolling bulk milk somatic cell count of 150,000/ml and 54 cows from the two organic herds, with average counts of 250,000/ml, were used. Antibiotics, cloxacillin or cephalosporin were used on treated cows at drying off.

"No cases of clinical mastitis were detected during the dry period in treated quarters in any of the herds. But in IAH untreated cows and organic untreated cows, seven out of 499 quarters and seven out of 172 quarters, respectively, had clinical mastitis caused by Strep uberis in the dry period."

New infections

As well as detecting clinical mastitis cases, Dr Berry also looked at how many quarters became newly infected with mastitis-causing pathogens during the dry period (see table). "Untreated cows were four times more likely to be infected at calving than treated cows.

"Of cows infected at calving, 50% went on to develop clinical mastitis within three months of parturition. So there remains a strong case for using dry cow therapy.

"Treated cows produce an extra 200kg milk over their subsequent lactation and there is at least a £30 a cow benefit to using dry cow antibiotics."

Organic herds should also consider dry cow therapy, she says. "Provided you can prove cows are infected with mastitis pathogens at drying off, it is possible to obtain derogations allowing antibiotic use.

"Treating infected cows also reduces the challenge from mastitis bugs to other cows which lie in the same areas as infected cows."

Proving cows are infected at drying off depends on showing elevated cell counts of more than 200,000/ml or conducting bacteriology tests, she adds.

Teat seals?

While she advises extreme caution over selectively treating cows with dry cow therapy on conventional farms, the prospect of an intramammary teat seal being marketed in the UK in the near future may make this a less risky option, she adds.

"But teat seals should only be used on uninfected cows, as they prevent new infections from entering the teat, but do nothing to cure existing ones."

Monitoring cell counts is the cheapest and easiest way to assess whether cows are infected, she says. "At least 50% of herds will have individual cell count information from NMR reports. But this can also be obtained using private labs at a cost of 50p-£1 a sample.

"Cows with cell counts of less than 200,000/ml are generally not infected with mastitis bugs. Ideally, monitor cell counts about five times over each cows lactation."

Treat all quarters

She advises treating all quarters at drying off and not selecting quarters. "There appears to be an animal effect. For cows left untreated at drying off there was an increased risk of a cow acquiring a new intra mammary infection in the dry period and also of acquiring infections in more than one quarter."

When administering dry cow therapy, make sure udders and teats are clean, she advises. "Wipe teats then clean with a spirit wipe, so they are sterile. Once cows have been treated keep a close eye on them. Treat for flies and watch for summer mastitis, pulling out any clinically infected cows, as these pose a risk to others.

"At calving, ensure yards are clean and dry, and calving paddocks are not overstocked. This will help reduce disease challenge to cows." &#42

&#8226 Risky to eliminate.

&#8226 Consider for organic herds.

&#8226 Promise from teat seals.

Ensure udders and teats are clean and sterile before putting in antibiotic tubes, says

Elizabeth Berry.


Group IAH herds Organic herds

No new New No new New

infections infections infections infections

Treated 424 19 144 0

Untreated 433 58 134 38