Nutro Products Inc. has restricted the sale of Greenies , canine and feline dental chews, to veterinary hospitals and pet specialty retailers, according to a FAQ section on Nutro's website.

Pet owners suggested that the treats were too difficult to digest because when some pets swallowed the chews whole, the treats became lodged in the pets' throats.

However, the company created a new  Veterinary Oral Health Council -approved, 96% digestible formula for the chews in 2006. Since the reformulation, no problems with the chews have been reported.

The website stated the reason for the restriction: " Each of the five sizes [of Greenies] is specially formulated to deliver the maximum dental benefit to each weight range."

"Pet medical professionals at veterinary hospitals and well-trained, knowledgeable staff at pet specialty stores are best equipped to ... make the right recommendation," Carolyn Hanigan, vice president of marketing at Nutro.