I personally would not do it. Funny thing is that I did at one time but it was not on purpose and was a very different case than most I think. I had 6 mini foals being weaned. I had a VERY OLD Quarter horse mare that I really thought needed to be put down because she had gotten so arthritic that she could barely lift her feet anymore. All she did for the last 2 years was shuffle her feet around just enough to graze alittle, get to her feed, and to her water, which we made sure were very close together.I wanted to have her put down but her owner, my guy, was just not able to handle that she was ready. She would spend all day long watching those foals. One morning I was horrified to see her at the other end of her field and the foals all running between her legs. Her head was down and I thought she was trying to figure out how to get them to leave her alone. Actually 5 were under her and the last one was running up and she would shake her head and he would run off and go to the back end. We sat and watched as they changed into a game of tag...big old mare appeared to be base. We werent sure how she got all the way to the other side of the field but put the little ones up and slowly led her back to her regular side of field. Next day they were all out again, next day the same. We noticed we were finding old mare all over that field and that she appeared to be moving much better. One night we hooked up a camera and watched her reach around and unlatch the babies gate... AH HA I knew there was no way they could have reached it!! I put a better latch on it that even she couldnt undo. She went back to sitting at the same end of field and doing nothing but getting more and more arthritic. I called vet out and asked him to check her out and asked him about if it would be bad for her to be walking all over the field with these babies. He said no that it was good for her if that was what was making her move more and therefore getting better. He didnt think she could lift her leg high enough to get any kind of a kick on them. The last year of her life she seemed to really enjoy. She had babies all around her. Even sleeping flat she was still base for them. She was happy being the babbysitter, we didnt have to worry they would hurt her, she moved more because she had her babies and it made her feel better physically and mentally. Seems strange that I would recomend not putting them together after I write all this, but if that mare had been a healthy running big horse, then I would have been worried about regular horse play causing a major accident. Goodness I was even worried that she would lay down or fall on one of them...
BTW She was humanely euthanized when the time was really right. The babies sure did miss their Big Mama though...