Privately held National Veterinary Associates has been sold to venture firm Summit Partners for about $128 million, the Westlake Village-based chain said.

National Veterinary, formed 10 years ago by veteran veterinarian Stan Creighton, does about $100 to $200 million per year in sales. Summit, a Silicon Valley-based firm, said it is now the largest owner of privately held vet clinics in the country.

Creighton formed National Veterinary in 1996. The chain now operates 96 animal hospitals in 29 states, including two in the Los Angeles area.