29 August 1997

HORMONE CURE FOR MASTITIS?

OXYTOCIN, the natural hormone which triggers milk let down, might be a cure for mastitis, but the story is likely to be far more involved than a simple flushing of bacteria from the udder.

Answers will come from a multi-centre programme involving the Hannah Research Institute, SAC, and Glasgow University. Funding of £55,000 has come from the Milk Development Council for the work and for an investigation into the efficacy of topical udder treatments for the condition.

Results will be reported at the British Mastitis Conference at Stoneleigh on Oct 8.

"The real aim is to gain an understanding of the way oxytocin works. It could be a non-antibiotic control of mastitis but it would involve daily injections for up to a week, which might be unacceptable at farm level," says Chris Knight from Hannah.

"American farmers have used large doses of oxytocin as therapy for early signs of mastitis. They found the hormone gave similar levels of cure to antibiotics. But there has been little research, and the assumption was that oxytocin worked by flushing out the udder and ridding it of the bacteria causing mastitis. "We think that is not the only possible explanation, and that oxytocin could trigger the cows immune system," says Dr Knight.

He explains that between the milk secretory cells and those outside carrying blood, body fluids, and the immune system, there are tight junctions. These open or leak when mastitis is present and also during early lactation when colostrum is being produced.

"We can monitor this leakage because milk contains more sodium than potassium, whereas it is the other way round in the blood; we can measure the ionic change in the milk," says Dr Knight.

"We also know that one of the effects of oxytocin is to squeeze the milk secretory cells, and that could open the tight junctions and cause the cows natural defence system to flow into the milk cells and kill the bacteria."

His research will determine whether it is this action, the flushing or a combination of both which is helping to control the infection.

That will be done by infecting individual quarters with low virulence staphylococcus aureus. The Hannah is geared up for milking individual quarters, giving the trial greater reliability than comparing one cow with another.

The treatments will compare oxytocin injection at milking, giving both extra let down and opening of tight junctions, and milking an hour later, when there will be no flushing effect but the tight junctions will still be leaking.

"We have measured sodium levels in the milk and found the dose of oxytocin needed to match the requirements of the experiment," says Dr Knight.

"We have only just begun the work, so it is far too early to say what the results will be, but anything which gets us nearer to a non-antibiotic treatment for mastitis has to be worthwhile," he adds.n

Cows testing positive for mastitis might, in future, be cured using oxytocin – the natural hormone which triggers milk let-down.