10 November 1995

Tougher test aims to keep the bugs at bay

Milk hygiene has never been more important, with premium pricing now a big incentive to secure a top quality product. This Special Focus examines how to achieve the high standards of cleanliness needed. Shelley Wright starts by looking at what the new hygiene test, Bactoscan, and the new somatic cell count rules have in store

THOUGH only somatic cell counts are included in the new European Directive, Milk Marque is determined to improve overall milk hygiene. It insists that further improvements to hygiene quality will be central to its continued success in the free market.

Milk Marque is the first of the UK milk buyers to introduce the new hygiene test, Bactoscan. It will replace the existing Total Bacterial Count test but Milk Marque stresses that the two tests are quite different and the Bactoscan results cannot be compared with TBCs (see below).

Mike Hurst, Milk Marques head of quality testing, says Bactoscan will give producers a more accurate result of the bacterial loading in their milk. And one of its main advantages is that it gives results in only five minutes, compared with the three days needed to complete the TBC test.

"The TBC test started in 1982 and uses a traditional plate count to measure the number of bacterial colonies in the milk sample. But, despite the name, TBCs did not give a total picture of all the bacteria. Bactoscan will pick up some bacteria that the old test missed," says Mr Hurst.

The TBC test used a small, known amount of milk in a laboratory dish with a nutrient jelly which allowed the bacteria to grow. The samples were then incubated for three days and the bacteria multiplied in colonies which could then be counted.

"Producers got a TBC reading that equated to the number of bacterial colonies a millilitre of their milk. Good quality has fewer than 20,000/ml, while bad has more than 100,000/ml," explains Mr Hurst.

But the TBC test could only detect bacteria that liked to grow in the particular medium provided and at the temperature chosen for incubation. The standards used were recognised internationally as the best compromise but some bacteria were missed.

Bactoscan is much less specific and can detect most bacteria, Mr Hurst says. "It gives a better idea of the level of bacteria in a sample and counts individual bacteria rather than colonies," he adds.

A tiny sample of milk is used by the Bactoscan machine. The whole process is automated. The milk is picked up by the machine and then cleaned to strip everything out except the bacteria. They are then stained and counted automatically. The machines – each costing about £100,000 – can process 80 samples/hour.

Because Bactoscan counts individual bacteria rather than colonies, the readings are much higher than TBCs. "Bactoscan readings are typically about five times higher than TBC counts, and it very much depends on the bacteria on a farm as to the relationship between the two readings," says Mr Hurst.

So though a producer may have good TBC results, he might not have such a good Bactoscan reading, simply because the new test picks up more. But Mr Hurst says that about 90% of Milk Marque producers are currently band A for TBC (fewer than 20,000 colonies/ml) and he predicts the same number will be in Bactoscan band A (fewer than 100,000/ml).

Milk Marque has been testing Bactoscan since June. And from last month through to next March producers will get both their TBC results and the Bactoscan reading for the same sample but they will continue to be paid on the TBCs.

From the start of the new milk year, next April, Milk Marque will switch over completely to Bactoscan. "So by next April, no member who is interested in hygiene quality should be unaware of the new test, and should be in band A," Mr Hurst says.

Milk Marques experience from early field trials with Bactoscan reveal that where on-farm hygiene is generally good then producers should be able to improve their results relatively easily.

Working with ADAS, Milk Marque suggests ways to correct any milk quality problems well before next April when its members will be paid on their Bactoscan readings (panel p46). &#42


Percentage of Milk Marque members/ comparative bandings

EstimatedTBCBactoscan

% membersreadingreading

(000)(000)

900-200-100

921-100101-500

1>100>500


Bactoscan payments from next April

BandBactoscanDeductions

result(p/litre)

A0-100nil

B101-5000.25

C>5002.0*

*6.0 if there has been a deduction of 2.0 in the previous six months. And 10.0 if there has been a deduction of 6.0 in the previous six months.