Michigan ? More than 300 dogs and cats may have died earlier this year as a result of eating contaminated pet food, a survey released Thursday shows.

There were no accurate counts earlier on how many pets had died from eating contaminated food, although estimates had run from a few dozen to several thousand.

The Michigan State University study showed the cause of death may have been related to melamine and cyanuric acid, two food contaminants that turned deadly when pet food manufacturers combined them.