Male dogs can breathe a sigh of relief thanks to researchers who have developed a reversible contraceptive that could avoid the need for neutering.

The implant, which makes dogs temporarily infertile, is expected to gain a European license within weeks. The £35 device stops male animals breeding and curbs any aggressive behavior by blocking production of testosterone and sperm.

It is expected to be of most use for dog owners who do not want to neuter their pets because they may want them to breed at a later date or are worried that they could suffer as a result of the general anesthetic required for surgery.

The implant, produced by Peptech, an Australian company, contains a drug called deslorelin, marketed as Suprelorin. This blocks the effect of a hormone, called gonadotrophin, which releases the (GnRH) hormone to control sperm production.

Katie Yeates, of Peptech, told New Scientist magazine: "The greatest advantage is that it's reversible. It gives you the option of breeding later and is an alternative for owners who don't want to put their animals through surgery."

Scientists at Peptech are working on an implant that lasts for 12 months and on similar products for cats and female dogs.

Oral contraceptives already available for female dogs have been linked to breast cancers and uterus infections.

David McDowell, a veterinary consultant at the RSPCA, said: "If dog owners are certain they don't want to use their pet for breeding, the RSPCA believes neutering remains the best option.

"However, if there is a good reason for an animal not to be castrated, for example it could be dangerous for health reasons for some dogs to have an anesthetic, or an owner knows they want to breed from their dog at a later date, then a reversible contraceptive could be considered instead."

The European Medicines Agency recommended in March that marketing authorization be granted to Suprelorin when Peptech's application comes before the European Commission - which is expected to happen before the end of this month.

Meanwhile, researchers in Brazil have decided the implants could be useful in totally different area. They are investigating use of the drug to temporarily sterilize cows, enabling their pregnancies to be timed with the availability of pastures.