16 October 1998

Swift intervention key to reducing mastitis costs

Treating mastitis before it

becomes obvious was a key

topic at last weeks British

Mastitis Conference.

Jessica Buss reports

TREATING cows with sub-clinical mastitis – before they show signs of infection – can reduce cell counts and prevent bugs infecting other cows in the herd.

That was the message of Devon dairy vet Andrew Biggs, the Vale Vet Centre, Tiverton, speaking at last weeks British Mastitis Conference at Kenilworth, Warks.

He believes it is more important to tackle sub-clinical mastitis to meet buyers increasing standards for milk quality. "A clinical case of mastitis is best seen as failure of control mechanisms on-farm."

When cows with a new sub-clinical mastitis infection are identified by a high cell count reading or persistently high cell count, they can be treated successfully with antibiotics.

Early treatment, before inflammation and milk clots are seen, often results in higher cure rates and shorter treatment duration.

However, care is needed when interpreting cell count results. Cows may not need antibiotics to cure infection as they can naturally fight mastitis bacteria, resulting in self-cured cases. Early treatment does not give the proportion of cows which would self-cure, and not suffer clinical mastitis, time to do so.

"Treating cows with sub-clinical infection eliminates a potential source of infection to other cows in the herd, reducing new mastitis cases. High cell count cows without clinical mastitis shed less bacteria than clinically infected cows. But they are more prevalent in the herd, so are a potent source of bacterial infection."

However, treatment must also depend on bulk milk somatic cell count, the number of cows affected, identification of bacteria present and cost of treatment. Vet costs and lost income from discarded milk must be weighed against financial penalties of high bulk milk cell counts, he added.

Mr Biggs suggested there was an apparent sub-clinical infection when a cows cell count, previously below 200,000/ml, increases to over 200,000/ml. But this may not lead to clinical mastitis because cell counts fluctuate daily. Monthly cell count trends or lab tests to identify bacteria strains are more reliable.

Identifying bacteria strains will allow management changes to help reduce the chance of continued new infections in the herd. Mastitis prevention should remain a priority, he stressed.

"While culling worst offenders is the best cure for mastitis and high cell counts, it does not address the cause of infection."

Mr Biggs also advised post-treatment checks, using bacteriological screening about one week after milk withholding ends or careful individual cell count monitoring.

But Ronald Erskine of Mich-igan State University veterinary college believed that unless sub-clinical infection was new or an easily cured bacteria type, treatment was unlikely to be economic.

He also said it was a mistake to treat repeat offenders when a quarter had not responded to therapy. And, when cows had more than one quarter infected or had an infected quarter for eight to nine months, cure rates were low. When a new infection was treated after three days 90% could be cured, but that reduced to 60% when treatment was delayed for 60 days.

SUB-CLINICAL MASTISIS

&#8226 Early treatment increases cure rate.

&#8226 Can reduce infection spread.

&#8226 Results should be monitored.