2 March 2001


Milk conductivity testing has become widely available over

recent years, but how useful is it? Jessica Buss reports

A PARLOUR that alerts a milker to the possibility of a cow having mastitis or high cell count would seem like a valuable bonus.

But it must be reliable enough to identify all cows with clinical signs, says Matthew Bartrop, herdsman for Peter Mills 140-cow herd at Alresford, Hants.

When a new parlour was fitted at the farm six years ago it came with a milk conductivity system which would take measurements from each cow during milking. The parlour computer analyses the results to identify any change in conductivity, indicating a possible variation in cell count or case of mastitis.

A report is available on the computer at the end of milking and an alert bleep sounds behind a cow in the parlour if there is a large enough % change in conductivity.

Mr Bartrop learned how to use the system provided, but after a few years of experience he reckons foremilking detects mastitis more reliably.

"Initially we looked at every cow with a raised conductivity and sometimes we werent finding a problem. Conductivity rose when cows were bulling, when a cow slipped in the yard and when we had cleaned out the sheds."

Then Mr Bartrop experimented with various settings on sensitivity which are varied according to cows stage of lactation. Cows in early lactation would be highlighted when their milk conductivity was 10% different to their 10-day average.

He also found that to keep the electrodes clean, milk-stone remover had to be used every fortnight rather than every month.

When a cow caused the system to bleep in the parlour with high or low conductivity, Mr Bartrop would check for visible signs of mastitis. It was too expensive to treat a cow in all four quarters, so he used a California Mastitis Test to identify which quarter had a high cell count.

A milk sample would also be taken from a cow with high conductivity for lab analysis, as is the farms practice with all clinical mastitis cases found.

"Initially, when the system was new, bacteriology identified some mastitis organisms. But once it settled, the lab found none, so we were spending money on tests with no results." A change in conductivity could also be caused by watery milk, he adds.

He then decided to only check cows which had two raised readings using an individual quarter meter loaned by ADAS Bridgets.

With this he could check all four quarters separately to find out whether one differed, and the cow would then be checked at the next milking. "When this second reading showed a problem a milk sample would be taken and the cow treated with antibiotics at the same time."

Mr Bartrop found the results using the quarter meter more acceptable. But he still had a major concern with the system missing clinical mastitis cases. "Frequently it didnt pick up a cow with a high cell count which was turning clinical. Possibly, her individual average was set too high because of her cell count so the system accepted mastitis was developing."

While he supports the theory of conductivity, it is a different story in practice. "When a cow gets mastitis, milk conductivity should go up and milk yield down. But the results on the farm have shown it to be misleading.

"We mainly find mastitis when foremilking. Conductivity is too vague; it cant identify the quarter."

Based on this experience cows are checked for visible signs of mastitis when a bleep sounds in the parlour. The cow health report produced by the computer at the end of milking is used to check highlighted cows at later milkings and to monitor progress.


&#8226 Quarter not identified.

&#8226 Mastitis cases missed.

&#8226 Foremilking more reliable.