18 September 1998

PRE-EMPTING ANTIBIOTIC CUT

Antibiotic use in dairy cows and welfare of heifers are

increasingly important issues covered by two projects

running at ADAS Bridgets, Hants. Emma Penny reports

INCREASING concern over resistance means that legislation limiting antibiotic use may be considered, particularly where they are used as a preventative measure.

But on-going Milk Develop-ment Council-funded research at ADAS Bridgets, Martyr Worthy, Winchester, Hants, aims to pre-empt any possible introduction of legislation which might reduce prophylactic antibiotic use.

Researcher Helen Biggadike says the project is looking for areas where antibiotic use for mastitis control could be reduced sensibly and without affecting welfare.

"Dry cow therapy could be described as prophylactic antibiotic use, and its an issue that the public is increasingly concerned about. In Scandinavia, antibiotic use is tightly controlled, and its possible that stricter controls will be adopted here – we are pre-empting the situation.

"The increase in organic production means we also need to know more about preventing or controlling mastitis without antibiotic use. Where antibiotics are used on organic farms, withdrawal periods are three to four times longer than recommended."

Two studies are being carried out. The first, funded by the Milk Development Council, was run on a large commercial dairy converting to organic production, explains Miss Biggadike.

"Using 150 cows, we monitored somatic cell counts and pathogens present in each quarter before drying off and at the start of the following lactation. We hoped to identify a pattern of pathogen and somatic cell count which would allow us to classify some cows as high risk of clinical mastitis and others as lower risk.

"So far, the only comment I would make is that it appears to be difficult to identify any link between somatic cell count and pathogens pre-drying off and clinical mastitis occurrence post-calving. We are now looking at the farms individual cow records – including cell count data – over a longer period to see whether there is a stronger link."

The second part of the trial involves 10 commercial herds using conventional dry cow therapy, with a minimum of 60 cows involved in the trial on each farm. Monthly milk samples from each quarter are analysed for cell counts in the last three months of one lactation and the first two months of the following lactation.

"We are looking at the pattern in individual quarters coupled with whole cow records where conventional dry cow therapy is used," she says.

Miss Biggadike plans to combine data from the organic and conventional trials to produce a predictive model of mastitis risk. "The aim to predict the result of a combination of a certain cell count, pathogen and treatment. This will include an economic analysis accounting for milk disposal, culling and treatment, and should be a practical guide."

However, she admits that the model may conclude that the current system of prophylactic dry cow therapy may be the best option. "But at least we will assess the options."

A third trial is also underway, looking at antibiotic treatment where mild clinical mastitis has occurred. This will attempt to assess when and whether antibiotic treatment is effective.

Not best option

Where there are visible clots in milk, but cows are not ill standard policy is to use antibiotics, but this may not be the best option – studies show that some of these cows would show a visible cure just as quickly without antibiotic treatment.

"We are carrying out pathogen analysis in all cases, as well as looking at that particular cows mastitis history. There may be times when we could reduce antibiotic input in mild cases without a subsequent increase in cell counts or mastitis severity."

All research has, however, shown that husbandry has a significant effect on mastitis occurrence. "Where all areas of management are good, cows are far less likely to be challenged by disease.

"Ultimately, we hope to pre-empt any legislation and to enable producers to control mastitis without incurring addition cost or compromising welfare," adds Miss Biggadike.

MASTITISTRIALS

&#8226 Reduce antibiotic use.

&#8226 Three-part on-farm trial.

&#8226 Produce prediction model.