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Swiss sheep could soon be texting shepherds for help when they are being stalked or attacked by wolves.

A Swiss biologist is developing a collar that can monitor a sheep's heart rate and spot when it is distressed.

The collar will call a shepherd if it spots that the heart rate of an animal has increased for an extended period.

Sheep are increasingly coming under attack by wolves in Switzerland and even those that survive often break fences and run miles as they escape.

Early prototypes of the collar, employing heart rate monitors similar to those used by runners to fine-tune their training, have been tested on 12 Swiss sheep. The tests, carried out in the Bernese Alps above Les Diablerets, involved scaring the sheep with two muzzled Czechoslovakian Wolfdogs.

This revealed that the resting heart rate of a sheep of about 60-80 beats-per-minute rises almost threefold when the animal is stressed.

Wolf expert Jean-Marc Landry from Swiss carnivore research group Kora came up with the idea for the collar in a bid to limit the number of sheep lost to wolves reaching Switzerland from Italy.

Growing numbers of sheep are being eaten by wolves, especially among small flocks owned by farmers who cannot afford a sheepdog. Even those that are not eaten trample down fences and flee long distances when being hunted.

Dr Landry said the first collars would be produced in the autumn and he was considering three different techniques to help protect the sheep.

The collars could be fitted with a mobile chip that alerted a shepherd via text message when the sheep were stressed. Alternatively they might play a loud noise or spray a chemical repellent to frighten off the wolf.

Other countries such as France and Norway have shown interest in the collar project.