The National Animal Supplement Council (NASC) found that 24 of the 87 brands it tested recently did not contain what was claimed, said council president, William Bookout, in an article from The Associated Press .

The NASC did not specify which brands, but instead used the results to help improve quality control.

"Sometimes a company doesn't even realize they have a problem, or a company can make an honest mistake," Bookout said.