Earlier the better. For the first five days the conceptus is just floating around. Best to ship a day or two after breeding, but be prepared to make a return trip if she's not in foal. I know people who have shipped from Florida to Kentucky, had the mare bred, and went back home the next day, with the mare checked in foal in 17 days.
I have lots of experience with this. I always left them until their 60 day check. No point doing it before they are checked in foal if you are just going to have to ship them back again.
Have to agree. I definitely wouldn't bother shipping back until they were at least confirmed in foal. I also always wait to ship a long haul until they are 60 days in foal. That being said, what do you consider a long haul? If it's only, for example, a four hour haul, I wouldn't have a problem trailering them back home after a 15 day check. But if you're talking more along the lines of Florida to Oregon, I would personally wait until the mare was 60 days in foal.
I moved my entire program from Texas to Georgia in July. My mares ranged from 3 days to 60 days in foal. We started everyone on Regumate for the trip, shipped air ride and didn't lose a single pregnancy. Good luck!
If the mare is content where she is..not nervous and well cared for, then I would wait 60 days before shipping her. As suggested, it would save you having to re-ship her if she doesn't take. If she is a nervous nelly then I would ship her right away. I had a mare that would not scan pregnant when I left her , but if I shipped her right away...she held the pregnancy. Her daughter was the same way. You might consider using regumate a few days after breeding her, it may help her hold onto the pregnancy if she has one.