The world's first "test tube" puppies born to a surrogate mother, is a breakthrough for conserving endangered species, scientists have said.
The seven beagle and cross-bred beagle-spaniel puppies have three sets of parents but all belong to the same litter.
Researchers from Cornell University pulled off this feat by fusing eggs and sperm in the lab to produce embryos.
The embryos were then inserted into a surrogate dog, perfectly timed with her reproductive cycle.
“Since the mid-1970s, people have been trying to do this in a dog and have been unsuccessful,” said Dr Alex Travis, the lead researcher.
One of the challenges Travis and his team faced included finding a way to prepare the sperm for fertilisation.
Normally, the dog's biology takes care of this stage.
However, the team soon learned that by adding magnesium to the cell culture, they were able to prepare the sperm artificially to ensure it fused successfully with the eggs.
Explaining the wider implications of this research, Travis said: "we can use this technique to conserve the genetics of endangered species.”
He said: "We can freeze and bank sperm, and use it for artificial insemination. We can also freeze oocytes, 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.
“With a combination of gene editing techniques and IVF, we can potentially prevent genetic disease before it starts.”
The study's results will also give scientists a better understanding of genetic diseases in humans too.