UPDATE 1-Canada's Pet Valu to be bought by U.S. group

*U.S. private equity firm to buy Pet Valu for C$143.7 mln

*Offer is C$13.68 cash for each share

*Pet Valu CEO Geoffrey Holt to retire when completed

*Shares last traded at C$13.05 on Friday (Adds details)

TORONTO, July 6 (Reuters) - Canadian pet food retailer Pet Valu PVC.TO said on Monday it agreed to be bought by a U.S. private equity group in a deal worth about C$143.7 million ($123.3 million).

The pet food and pet-related supply retailer, with about 300 stores in Canada and the United States, said Atlanta-based Roark Capital Group plans to offer C$13.68 cash for each share. The shares last traded at C$13.05 on the Toronto Stock Exchange on Friday representing a 4.8 percent premium.

Some of the company's biggest shareholders, including Geoffrey Holt, its founder and chief executive, have agreed to tender their shares to the offer.

Holt has also agreed to retire as chief executive once the transaction is completed.

The deal, which is subject to shareholder and court approval, is expected to close in the third quarter. ($1=$1.17 Canadian) (Reporting by Scott Anderson, editing by Maureen Bavdek)