MONDAY, Jan. 30 (HealthDay News) -- Ultrasound equipment used for physical therapy may have potential as a male contraceptive, according to a new animal study.

Based on their findings with lab rats, the researchers said it's possible that the commercially available equipment could make men infertile by lowering their sperm counts.

In conducting the study, researchers from the department of pediatrics at the University of North Carolina School of Medicine rotated high-frequency ultrasound around male rat testes, warming them to 37 degrees centigrade (about 98.6 degrees F). They found two 15-minute ultrasound sessions two days apart were most effective, resulting in a sperm count index of zero.

The study is published Jan. 29 in the journal Reproductive Biology and Endocrinology.

"Unlike humans, rats remain fertile even with extremely low sperm counts," said James Tsuruta of the UNC School of Medicine, in a journal news release. "However, our noninvasive ultrasound treatment reduced sperm reserves in rats far below levels normally seen in fertile men (95 percent of fertile men have more than 39 million sperm in their ejaculate)."

Tsuruta said more research is needed to determine how long sperm counts would remain low and whether or not the ultrasound procedure is safe for more than one use.

While studies involving animals can be useful, they frequently fail to produce similar results in humans.

More information

The U.S. Centers for Disease Control and Prevention provides more information on existing forms of contraception.