A dose of ultrasound to the testicles can stop the production of sperm, according to researchers investigating a new form of contraception.

A study on rats published in Reproductive Biology and Endocrinology showed that sound waves could be used to reduce sperm counts to levels that would cause infertility in humans.

Researchers described ultrasound as a "promising candidate" in contraception.

However, far more tests are required before it could be used.

The concept was first proposed in the 1970s, but is now being pursued by researchers at the University of North Carolina who won a grant from the Bill & Melinda Gates Foundation.

They found that two, 15-minute doses "significantly reduced" the number of sperm-producing cells and sperm levels.

It was most effective when delivered two days apart and through warm salt water.

Among the 78 research projects to receive $100,000 grants from the Bill & Melinda Gates Foundation earlier this week as part of the Grand Challenges in Global Health initiative, is an effort by researchers at the University of North Carolina, Chapel Hill, to develop a non-invasive, reversible form of birth control for men — using ultrasound. Based on preliminary trials in rats, researchers James Tsuruta and Paul Dayton hope to develop a technique that would render men temporarily infertile for up to six months after one or two ultrasound exposures.

The project is one of 10 to receive grants toward the goal of creating new technologies for contraception. Other projects geared toward men include a male contraceptive pill that researchers say would work by limiting the maturation of sperm, and research into the specific chemical compounds in the vagina that guide sperm to egg — which researchers hope to recreate in the lab and potentially use to “disrupt” sperm navigation en route to the egg. (Earlier this year, researchers at the University of California, San Francisco uncovered clues about how pH levels impact how sperm swim, and expressed hope that further research in this arena could yield possibilities for male contraception as well.)