24 March 2000

Oxytocin shows promise in fight against mastitis

By Jessica Buss

INJECTING the hormone oxytocin has proved as effective as antibiotics against one of the most difficult mastitis bugs to kill, Staph aureus, in a recent experimental study.

The study at the Hannah Research Institute, Ayrshire, compared four treatments on cows infected with Staph aureus mastitis bacteria, according to researcher Chris Knight.

"Staph aureus is the most difficult mastitis bug to get rid of, as it forms micro-capsules to protect itself and can remain in the udder for months before infection flares up."

It is a prevalent bug and is a major cause of sub-clinical mastitis, adds Prof Knight.

The most commonly used treatment is a course of antibiotics, but in the study, injecting a large dose of oxytocin proved as effective at controlling the bacteria.

Both these treatments resulted in a 50% to 70% fall in Staph aureus bacteria present. The other treatment of massage with a proprietary liniment resulted in only a 10% drop, with twice as many quarters remaining infected after liniment than either oxytocin or antibiotic.

Oxytocin could have advantages for producers, as it has no withdrawal period, so once milk is clear of clots it can be sold, he says. "There is also concern about overuse of antibiotics – mostly by GPs and in animal feed – and although they are still accepted for therapy that may not be the case in future."

Oxytocin is known to help animals let-down milk, promoting emptying of the udder and removal of bugs. But Prof Knight believes the larger dose used for the study may have additional benefits. It is possible that it also helps enhance the animals immune response.

He says oxytocin appears to open the tight junctions between neighbouring mammary cells. These close once they have let antibodies into the milk for the calf in early lactation. These tight junctions also loosen when cows have mastitis, possibly allowing antibodies in to fight infection naturally. This theory forms the basis of conductivity tests for early mastitis detection, he adds.

"But using oxytocin for too long could result in permanent damage to the secretory cells in the udder. We still need to identify the correct dose and treatment time before we can recommend the treatment on farm. In the trial we used oxytocin for a week at 100iu and that was probably too long."

Although oxytocin is used to treat mastitis in the US, more research into its effect on cows in late pregnancy and the oestrous cycles of cows in early lactation is also needed, he adds.

"But neither oxytocin nor antibiotics are particularly successful at getting rid of this bug. Only about 10% of quarters were totally cleared of infection after either treatment in a series of tests. If we had only taken a single sample after treatment it would have indicated 50% were totally clear – showing the limit of taking a single sample," saysProf Knight.

It is also possible that a strategy using both antibiotic and oxytocin could be more effective in clearing Staph aureus infections, he adds.

Of the other two treatments, massage could be helpful in ensuring the udder is completely emptied. But this effect was not increased by using liniment, he adds.

lThis study was funded by the Milk Development Council. &#42

MASTITIS STUDY

&#8226 Oxytocin effective.

&#8226 Large oxytocin dose needed.

&#8226 Liniment not helpful.

New research might lead to new treatments against mastitis caused by Staph aureus, believe scientists.