As three New York auction houses prepare sales of dog art, there have probably never been as many pooches — most portrayed in 19th-century paintings, porcelain, and bronzes — ready to bound onto the market. The Westminster Kennel Club Dog Show kicks off Monday at Madison Square Garden. Meanwhile, the Frick Collection is preparing “George Stubbs (1724–1806): A Celebration,” an exhibit opening next Wednesday in which five of the 17 paintings on view will depict dogs.

“It’s the perfect centerpiece for dog-in-art sales,” the vice president of fine art at Bonhams New York, Alan Fausel, said of the Westminster competition, which draws 20,000 dog enthusiasts each day from around the world. (Mr. Fausel created the specialty dog art auctions nine years ago when he worked at a rival auction house, Doyle New York.) Bonhams will hold its annual Dog Sale on Tuesday, with 234 lots on the block. Doyle will mount its ninth annual Dogs in Art auction, with 141 lots, the same day.

Christie’s is capitalizing on those events by previewing 20 paintings from its first Dog Sale, which will take place June 22 at its Rockefeller Center headquarters. The preview is slated for Monday and Tuesday at Christie’s Private Sales Gallery on East 67th Street. “Most of the paintings come from the English era of dog portraiture, which Queen Victoria popularized,” a specialist in British art at Christie’s, Clare Smith, said of the works that house will offer.

Dog art goes for high prices, although paintings by Stubbs, whose work sells in the millions, is in a class by itself at auction. More than a decade ago, many examples went for around $1,000 or less. But the genre is fast picking up steam. Last year Mr. Fausel hammered down John Emms’s 1898 oil painting “New Forest Foxhounds” for a hefty $842,250, striking a world record for the niche category. “Now, serious collectors of dog paintings — with 15 or more examples — are not unusual,” he said.

Price hikes are not limited to the high end of the market. “The price blip covers the entire spectrum of the market,” Mr. Fausel said. “Dog prints by the 20th-century artist Marguerite Kirmse used to go for $200, but now each can bring $1,000 or more.”

Small bronzes, ceramics, and dogtopped canes are also part of this growing market,” the vice president and executive director of paintings at Doyle, Elaine Banks Stainton, said. She said she expects a 2 1/8-inch-high silver pug, made by a generic Russian artist, to jump past its $800–$1,200 estimate.

“The American taste for pet portraiture has waxed and waned,” a professor of art history at Barnard College, Anne Higonnet, said. In the early 1900s, small bronzes were popular. By the 1940s and ’50s, that fad slipped into obscurity. Lately, prices have been inching up although the market remains predominantly middlebrow, sniffed at by collectors of fine art.

Ms. Higonnet said she believes the spike in interest for paintings of small dogs corresponds to the current popularity for “small handbag dogs.”

One Upper East Side dog art dealer, William Secord, has written three books on the topic.

“When I started, there were no books, none at all,” Mr. Secord said. His book “Dog Paintings 1840–1940: A Social History of the Dog in Art” (Antique Collectors Club, 1992), which includes 400 images of dog art, is now in its sixth printing, and Mr. Secord is revising the text for yet another printing.

Just as it does in kennels, breeding counts in dog portraiture. “Certain breeds command a higher value,” Mr. Fausel said. Portrayals of pointers, setters, and pugs command the highest prices. Thomas Blinks’s oil painting “Setters,” which had belonged to the Stock Exchange Club of Melbourne, is pegged to fetch between $100,000 and $150,000 at the Bonhams auction. The price is high, in part, because the artist had exhibited at London’s Royal Academy.

With the widening of the market, contemporary portraiture is also becoming more popular. The Upper East Side gallery Frost & Reed is currently holding its fourth annual “Dogs in Art” show, which features contemporary canine art. Mr. Secord’s gallery is showcasing selections of vintage art as well as work by Constance Payne, a Buffalo, N.Y.–based artist whose work is priced between $2,500 and $24,000.

Commissions for original paintings depicting favored pets are also increasing in number. Mr. Secord said his most expensive commission so far has been an oil painting of three golden retrievers done by Christine Merrill for $35,000. Why the spurt in special-order paintings? “People increasingly think of dogs as members of the family,” Mr. Secord said. And family members deserve family portraits.