Sometimes it's to put a big lamb in a ewe that's bigger than its natural mum, yes.
Sometimes - more often, I think - it's to create more offspring from one really good tup (and really good ewes which are hormonally flushed, too) than could be achieved [more] naturally.
And both together, of course. Huge numbers of offspring from a smallish nucleus of excellent (depending on your definition
) meat sheep, embryos carried and lambs born to and raised by other sheep with good capabilities in the lambing and rearing departments.
Same thing's been happening in double-muscled cattle for a while, Jerseys are often used as the recipient / surrogate mother as they have a very wide pelvis and produce fabulous milk which will make a great job of the calves. More recently, however, the calves have become so darned large (being limited only by the size of the Jersey's birth canal, not that of their genetic mother) that they now do elective caesarians rather than risk the calf getting stuck. So now there are no limits on how large a calf they can breed, except maybe the Jersey's stomach muscles... The vet has told us that 2 caesarians is as many as a cow can have, so if that's still true, then the Jerseys are presumeably used twice.
I've no idea whether they ever implant multiple calves...
(Derailing a bit, but this is why my not-for-breeding Jersey heifer is becoming boxed meat this weekend, and didn't get sold alive.)
I accept it with misgivings when it's about saving a rare breed or bloodline, and with slightly more misgivings when it's about bringing in 'improved' bloodlines, but start to feel very uncomfortable when the surrogate mothers are more capacious than the natural mothers (for the reasons given above in the Jersey story) and when it is used as a regular breeding practise, when it feels too much like using ewes as a unit of production - real 'factory farming'. (Echoes of that pig unit in the 70s. *
:shudder:*)
Topic: Embryo Transfer (Read 8477 times)
