8 November 1996

Cross

contamination countered

THE secret to reducing cell counts from 250,000 to 150,000/ml lies in minimising cross cow contamination and identifying and treating high cell count cows.

So says Hampshire vet Jonathan Harwood, St Peters vet group, Petersfield.

"High cell count cows shed bacterial infection and this is passed onto other cows by milkers hands and the liners. The liner then becomes contaminated and the older and more cracked it is the more infection it will hold."

Mr Harwoods client Nick Lambert, Manor Farm, Langrish, Petersfield maintains cell counts below 250,000 and Bactoscan readings at about 35 all year round. Its a performance that secures him a top price for hygienic quality.

The pre-milking routine for the 100-cow herd includes dry wiping each cow with a clean piece of paper towel and stripping the foremilk. This aids early mastitis detection and helps reduce cell counts. But on the flip side it is at this point that milkers hands present highest risk of contamination.

"Milkers should wear gloves," says Mr Harwood. "Gloves have a smaller bacterial population since theyre not full of cracks and crevices like hands. Even washing hands in soap doesnt kill bacteria.

"Modern latex gloves can be changed frequently, fit better than rubber washing-up gloves, and can be dipped in disinfectant."

But because Mr Lambert dislikes wearing gloves, and finds it difficult to sense muck on them, Mr Harwood has suggested he installs a bactericidal soap dispenser. "This is better than ordinary soap but should ideally be applied for 2min," he says. When this soap was unavailable washing hands in disinfected udder washing water was another option.

And although fore-milking was useful to identify mastitis it could spread infection. "Ideally a whole line of cows should be fore-milked and then the teats cleaned."

Infection could also be spread during milking by cross contamination of liners. When a high cell count cow is milked she contaminates the liner and this can then contaminate the next seven cows, warns Mr Harwood. "The only way to clean the cluster is with water at 85C for 5secs. Flushing through with cold water has no effect." He suggests milking affected cows last to avoid contaminating liners. Cows could also be contaminated through poor milk flow, back flow from a neighbouring teat cup when clawpieces were too small, or due to teat end impaction caused by vacuum fluctuations.

Good vacuum and pulsation prevent teat end damage and herds with cell counts under 250,000/ml are unlikely to have damaged teats, says Mr Harwood.

Mr Lambert ensures his milking plant is thoroughly serviced twice a year. If this doesnt reduce cell counts, Mr Harwood advises carrying out a dynamic test during milking to check teat end vacuum.

Post-milking cows are sprayed with an iodine-based product. Mr Harwood considers careful dipping or spraying essential. "It is easy to spray badly and get poor teat cover and it uses more solution than dipping so is more expensive," he says.

"Dipping is slower but you immerse the whole teat, you just need to keep the dipping cup clean."

A further aid to cell count control is monthly individual cell counting. But according to Mr Harwood it is essential that the cows are ranked on % inclusion in the bulk tank for which yield recording is also needed. For example, a late lactation cow will tend to have a higher cell count.

He suggests comparing three or more months figures rather than basing any decision on one reading.

"When you want to maintain a 150,000 cell count you will need to be more critical of individual cows and decide whether to treat or cull them.

"When keeping a high cell count cow then send a sample for bacteriology and antibiotic sensitivity. Your vet may recommend prolonged tubing for up to three weeks or antibiotic injections close to drying off and a long acting dry cow tube."

Mr Lambert uses DAISY milk recording and currently 20% of the bulk milk cells are from two cows. For consistently high cell count cows a California Milk Test is used to identify the affected quarter and then cows are milked on three-quarters.

"We dont lose that much milk and keep the cow going until she has her next calf," says Mr Lambert.

The most difficult period at Manor Farm is in late summer when cow yields decrease before drying off for autumn calving. This is difficult for block calving herds to avoid, says Mr Harwood, for cell counts are always higher in late lactation.

Monitoring individual cell counts could allow some of the higher cell count cows to be dried off early. Another option was to extend the calving pattern.

Nick Lambert aims to keep cows clean outside the parlour so they only need dry wiping before milking.

Damaged teat cup liners increase bacterial contamination between cows, says Jonathan Harwood.


Producers supplying Milk Marque will be offered an extra 0.2p/litre for cell counts below 150,000 and an extra 0.2p/litre for bactoscan readings below 50 from next April. Those that maintain these standards for a whole year earn another 0.2p/litre.