The phrase "pig embryos" refers to the early stages of unborn baby pigs. These embryos are the beginning of pig development before they are fully formed. Full definition
In an application for a prestigious «Pioneer Award» from NIH this year, he proposed injecting human pluripotent stem cells into pig embryos whose genes for specific organs had been knocked out. (statnews.com)
To test the idea, Yair Reisner at the Weizmann Institute in Rehovot, Israel, and colleagues, gave two diabetic monkeys pancreases from pig embryos. (newscientist.com)
The modified cell nuclei were then inserted into unfertilized eggs to create engineered pig embryos, which were implanted in a normal sow. (discovermagazine.com)