I have been asked to breed to 2 bulls for flushes many times, it works if you do things correctly and are ON TIME
I only breed the donors ONE time, but I horn breed them fairly deep, at least a long ways past your normal A-I point.
I put one comple straw into each uterin horn LATE in the cycle, at least 6 and often longer after all standing is done.
Doing this allows the semen to have less travel distance, gets it past all the mucus build up in frint of the cervix on these superovulated donors, and allows for more viability time when they do get to the ovaduct.
There was a picture or two on here a few weeks ago of a coule ET calves for Dusty -- that cow was bred to Carnac and Vegas for the flush. There was no doubt that the resulting eggs from each sire were correct. Pretty neat stuff.
There has been several donors here that I onlyhad one straw of semen for - period! When that happens, I make sure the timing is right and simply horn breed her with 1/2 straw per side. I have never seen the need to breed more than onceif you get the timing right AND you have excellent semen quality to start with.
These places can do what they want, it's thier privoledge, but it is for the most part not necessary to breed them more than once and for certain, no drugs are needed at breeding. We don't always get every egg to be good quality, but we do get along very well on fertilization, with minimal input!
The 2 sire breeding works, but unless you use two different sire lines -- especially on purebreds, you may still need to do the DNA to be sure. I give it 95% or better accuracy if done like I do it here!
Good luck to all!
Terry