With rescue dogs all the rage and shelters overflowing with homeless dogs, it seemed a little ironic to hear veterinarians talk Saturday about how to solve canine fertility problems.

But their audience was a serious, sophisticated group of about 40 dog breeders who had traveled from as far away as North Carolina to learn about reproduction, genetics, behavior, and the dog microbiome at a scientific conference at the University of Pennsylvania.

Specialized vets now monitor hormones closely to improve the odds of conception. They use ultrasound to check the developing fetuses. Breeders have fetal monitors at home for high-risk moms. Should you have a particularly valuable male, it's now possible to retrieve his sperm after he dies - if you do it fast enough. For the stud dog who is not, well, all that studly, there are tons of tests to figure out what's wrong with him or his sperm.

A little doggy therapy may also be in order. Timing is everything in dog mating, and a poorly timed rendezvous with one snarling bitch (we're using the technical term for a female dog here) can really put a male dog off his game. "If the female turns around and bites him, that might turn him off for the rest of his life," said Margret Casal, associate professor of medical genetics at Penn Vet.

Nobody likes puppy mills, but Casal said high-end breeders like the ones at the Penn conference are making the health of their pups a priority. About 70 percent of the dogs vets see in clinics are purebreds, including the rescue dogs. People like the fact that purebreds have predictable physical and personality traits. "People already know what they want in a dog, and that's why they'll get a purebred dog," she said.

She said it's a myth that mixed-breed dogs are healthier. "Hip dysplasia is just as common among mutts as it is among purebred dogs."

Cindy O'Connor, a Massachusetts vet who focused on female fertility issues, is herself a breeder of Portuguese water dogs. She told the group it is important for them to work together and to breed with the "genetic wealth of the breed as a whole in mind" rather than one trait.

Later, she said many breeders have devoted their lives to producing healthy animals. "The people in this room that are breeding dogs, those dogs never end up in shelters," she said.

Elaine Ostrander, an expert on canine genetics with the National Institutes of Health, has found the detailed pedigree records of breeders - and the genes of the specific breeds themselves - invaluable in pinpointing genes that cause cancer and physical differences.

"You never get pedigrees like that for people," she said.

One of her group's studies stemmed from breeders who told her that black standard poodles, not white ones, were getting a form of squamous cell cancer under the nail beds. She knew that a bad genetic signal was "piggybacking" on the genes related to coat color.

Barbara Penny, who breeds English cocker spaniels in Worcester, wanted so badly to come to the conference - it was "terrific in terms of genetics" - that she brought along one of her puppies, a tiny blue roan who mostly entertained herself in a playpen at the back of the auditorium.

"I couldn't leave her at home because I feed her every two or three hours," Penny said.

Not yet six weeks, the puppy also got a checkup with the Penn veterinarians who delivered her by cesarean section after what had been a high-risk pregnancy for her champion mother. In a shock, the pup was born with a cleft palate and only one eye. She couldn't nurse properly so Penny hand-fed her.

"We try our best to breed healthy, wonderful purebred dogs," Penny said.

"She won't have a career in the show ring and she will be spayed." What she does have is a "wonderful personality."

Penny decided to keep her. The puppy is the last of her line and she was born a week after Penny's co-breeder, John Casavecchia, died of a brain aneurysm.

Penny named the pup in his honor: Cassie.