More than a half century of breeding, exhibiting and judging show dogs has finally brought M. Josephine Deubler to this: She will determine exactly who is top dog this year.

Deubler is somewhat of a rare breed herself. An assistant professor of emergency medicine in the School of Veterinary Medicine's Clinical Studies Department, the first female graduate of Penn's School of Veterinary Medicine has been selected to judge Best in Show at this year's Westminster Kennel Club show in New York Feb. 16 and 17.

The 122-year-old Westminster show is the oldest and most prestigious dog show in the country. Competition for entry, which is limited to Ameican Kennel Club champions of record, is fierce: all the available slots for this year's show were filled less than an hour after entries opened. Deubler will choose the best all-around performer from 2,500 dogs representing all 153 AKC-recognized breeds.

To become a Best-in-Show judge takes years of dogged effort. "Before you can judge Best in Show, you have to be approved to judge at least one of the seven groups: Sporting, Hound, Working, Terrier, Toy, Non-Sporting and Herding," Deubler said. "In order to be a group judge, you must be approved to judge all the breeds in a group. And in order to judge a breed, you must first engage in some activity in your basic breed. You need to raise a certain number of champions, demonstrate some experience, and then go from there."

Deubler's dog days began with raising and exhibiting Dandie Dinmont Terriers in the mid-1940s. In 1962, she became an AKC-licensed judge for the breed. Since then, she has qualified to judge all 51 breeds in the Hound and Terrier groups. In addition to her work as a judge, she chairs the show committees for two area shows: the Bucks County Kennel Club show, the country's largest outdoor show, and the Montgomery County Kennel Club show, the world's largest terrier show.

Deubler herself has known about the Westminster's honor for two years. "When the show committee asked me to serve as Best-in-Show judge, I was totally surprised," she said. "I had to keep it a secret for a year, until they announced it last May."

While every dog will have its day at Westminster, only the leaders of the pack, including Deubler, will make it onto television. Much of the judging will air live on the USA cable network on Monday and Tuesday, Feb. 16 and 17, at 8 p.m., with Best in Show on Tuesday.