Seven puppies, all the result of in vitro fertilization, have been born in the culmination of an effort that dates back decades to the 1970s.

After 19 embryos were transferred into the host mother beagle, resulting in seven viable pregnancies, the litter was delivered by Cesarean section.

The IFV procedure yielded two puppies from a beagle mother and a cocker spaniel father, with five from beagle mother and father pairings, the researchers report in the journal PLOS ONE.

"Since the mid-1970s, people have been trying to do this in a dog and have been unsuccessful," says Alex Travis, a professor of reproductive biology at Cornell University's College of Veterinary Medicine.

In IVF, collected eggs and sperm are brought together in a lab to create embryos that are then implanted in the female reproductive tract.

Long common in humans, the procedure has long been tried in dogs but has proved difficult because canines have a reproductive system different from other mammals, the researchers explain.

Eggs collected from female dogs at the same point in cell maturation timing as seen in other animals failed to fertilize because they proved too immature, they said, so they learned to leave the eggs in the female dogs several additional days, resulting in a greatly improved fertilization rate.

They also had to treat dog sperm with chemicals meant to mimic what happens when sperm enter the reproductive tract of females.

"We made those two changes, and now we achieve success in fertilization rates at 80 to 90 percent," Travis says.

The successful IVF births have significant implications for conservation of wildlife, experts say.

"The reason for doing things like this is that it will lead to the preservation of species that are almost lost," says Margaret Casal of University of Pennsylvania School of Veterinary Medicine.

"Canid types — wolves, foxes — certain sub-species. There are many different types. They may not be facing extinction just yet but some are running into a crisis," she says.

Travis is quick to agree that the technique could prove valuable as a conservation tool.

"We can freeze and bank sperm, and use it for artificial insemination," he notes. "We can also freeze oocytes [eggs], but in the absence of in vitro fertilization, we couldn't use them. Now we can use this technique to conserve the genetics of endangered species."