Yes, as others have said, a lot of complete misinformation. TB mares are NOT separated from their foals prior to a proper weaning age unless by death, rejection of the foal, or some other very serious situation. Mares are NOT separated from their foals so that they can be re-bred. Well, ok, they might be separated for a couple of hours while the mare goes to the breeding shed, but no nurse mare is required for that!
Nurse mares are very expensive to use and require work and supervision for the introduction. It’s not like you can just put the two together and it’s a done deal. It can be risky for the foal and it’s not ideal, just the best way many farms are able to handle a very dire situation such as when a mare dies or attacks her newborn. Farms use nurse mares because raising orphan foals is a very specialized thing. I’ve done it and can say from experience that it was a steep learning curve with a lot of mistakes the first go round.
There are some very excellent posts on this thread that explain the situation well.
In any case, rest assured that live cover in no way increases the use of nurse mares, that’s just pure fantasy. Foals are shipped with their dams to locations at or near where they will be re-bred. Most farms charge only minimal charges for the board and care of that foal–definitely totalling MUCH less than what it costs to get a nurse mare.