i use cows that milk well, are good mothers and concieve easily. Can be any breed but usually angus based since that is what we raise. they also will be cows that may have a structural flaw or pedigree that we do not care to pass on.
I don't know how important EPDs are to you, but in the US, Angus ET calves don't have EPDs unless the surrogate dam is a registered Angus with EPDs. That might be something you'd want to look into before you select a cow to carry an embryo.
This is only based on our experience; nothing scientifically proven. My experience has been that you are best to use recips that have a similar gestation length to the breed of embryos that you are implanting. The calf is usually the intiator of birth therefore the breed of the calf inside has a direct effect on gestation length.
We used to raise Blonde d'Aquitaine in the 80's and 90's. They normally had about a 290-292 day gestation and calved in the 95-105 lb range. That would not be a problem for a mature Angus cow; our Angus cows calved around 280 days and had similar sized calves 85-95 lbs (100% angus). When we put our Blonde embryos in the Angus cows their gestation increased to over 290 days; problem was the calves were 110-120 lbs or larger. I believe that, although the calf initiates birth, the cow feeds the calf in her womb as if it was 100% angus???? I think the Angus cows provided nutrients to the calf inside them as if they were going to be born at 280 days, problem was that it was a Blonde calf to be born at 290 days, basically 10 days past what the Angus cow expected = much larger calves.
I think what I am seeing is real as this is based on several years of data with different genetics and different recips (mostly angus or angus cross). We have not had any such problems putting Angus embryos into Angus cows so it doesn't seem to have anything to do with the transplantation procedure itself. Anyone else had similar experiences?
When doing our holstein Et's the most important thing to us is that the heifers are fertile, cycling and both ovaries are viable. The most important thing when doing ET's is getting the embryo to settle and getting a live calf out of it. If the heifer does want the calf when born you can easily bottle feed it..Which does happen on occasion. The risks are high enough that I would never use anything other than a heifer not even a second calver, also the odd c-section is cheap when you look into the cost of flushing and transplanting, but this would be a rare occasion . All of our heifers to be used for ET are checked thoroughly by our vet.