Cows that are massaged in a "cow wash" will produce more milk, the makers of the animal grooming system said Wednesday.

The giant yellow rotating brush boosts milk production in herds by three and a half percent, said DeLaval, the Swedish dairy farm supplier behind the device.

The product, which is fitted to milking sheds, is already used in 30,000 dairy farms across Sweden and works by improving the animals' blood circulation with the massaging effect of its bristles.

“The swinging cow brush is a self-grooming device that keeps cows happier, healthier and more productive," said a DeLaval spokesman.

“The brush starts to rotate on contact at an animal-friendly speed. It swings freely in all directions, smoothly up, over and alongside the cow.

‘’The bristles have the right length and hardness to stimulate the blood circulation whilst helping the cow to keep clean and calm.

‘’It is very popular among dairy farmers. Cows using the swinging cow brush are cleaner, calmer and therefore more balanced.’’

A study by New York’s Cornell University last year also found that brushing cows resulted in better health due to an increase in blood circulation.

It concluded that cows using the DeLaval machine were 34 percent less likely to suffer from clinical mastitis, a painful condition which can reduce milk yields.