Dr Metcalf in Australia flushed eggs in dogs over 15 years ago and also froze embryos using those eggs. He did flush eggs from a female that did not conceive anymore bc of age, and fertilized those. All the eggs she had left (memory a bit fuzzy, but I think was many, many - much higher number than released in a normal season). From what I remember from talking to him 12-15 years ago was that the problem was constructing an artificial uterus to grow the embryos. For other animals it was easier than for dogs. He did stop research and went into private practice. He had offers from US universities to come and continue the research, but I think after doing only research for years the terms were not good enough. The status then was that he could take eggs from one female, fertilize with semen and implant into another female. It worked, but only when both females were in exact same stage in their season. So for most practical purposes was not feasible. I remember I asked about transporting the embryos and one could actually implant them into rabbits, ship the rabbit and take out the embryo again when received (-; But did not solve any other problem than transport (plus PETA would not like that one (-: ).
So the basics have been done long ago, but the resources have not been found to do enough research on how to grow the embryos outside the uterus until the could be frozen in a state where they could be used as with for example cattle. I am no vet and might use some very layman terms recalling these conversations from very long ago.