Experts believe dogs and cats may have more medical emergencies when the moon is at or near its fullest.

A full moon may be responsible for more emergency room visits by cats and dogs, according to a study conducted at Colorado State University's College of Veterinary Medicine and Biomedical Sciences. Raegan Wells, DVM, and her colleagues believe dogs and cats may have more medical emergencies when the moon is at or near its fullest. The study appears in the July 15 issue of the Journal of the American Veterinary Medical Association.

To reach their conclusions, researchers compiled data from 1992 to 2002, looking at nearly 12,000 case histories of cats and dogs treated at the university's Veterinary Medical Center. The data suggests that the risk of emergencies on fuller moon days was 23 percent greater in cats and 28 percent greater in dogs when compared with other days. The increase was most pronounced during the moon's fullest stages: waxing gibbous, full and waning gibbous.

"If you talk to any person, from kennel help, nurse, front-desk person to doctor, you frequently hear the comment on a busy night, 'Gee, is it a full moon?'" said Wells, an emergency and critical care medicine resident in the Department of Clinical Sciences. "There is a belief that things are busier on full-moon nights."

The reason behind the correlation between emergency-room traffic and the full moon isn't clear, Wells said. She also noted that the data did not indicate an increase in aggressive behavior in pets during a full moon.