I ride all of my mares during pregnancy. I usually have them bred in April and May, ride them all summer, then when the weather gets colder I stop riding for the winter. So, that would be up until they are about 7 months pregnant. Two years ago I took them on a camping trip while they were 5 and 6 months pregnant. The difference is if they are used to being ridden all the time like mine. I would never take an unconditioned pregnant mare for a long trail ride.

Obviously when they get HUGE (9-10 months pregnant) I wouldn't ride them, because like you said Linda, I know I wouldn't want to be hugely pregnant and have weight on my back.