"Suppose one of you has a friend, and he goes to him at midnight and says, 'Friend, lend me three loaves of bread, because a friend of mine on a journey has come to me, and I have nothing to set before him.' Then the one inside answers, 'Don't bother me. The door is already locked, and my children are with me in bed. I can't get up and give you anything'." (http://www.unhinderedliving.com/bed.html)
The above site goes on to tell of the bed made for the royal family in England that could sleep 102 people in the 1600s! Clearly co-sleeping was not only practiced by poor peasants, but was the norm for everyone!
So I honestly do not believe that with wild animals around and strangers coming to check out her babe, Mary would wrap up her newborn and lay him down to sleep in a manger. Nay (neigh!), I think the mention of the manger was perhaps referring only to the fact that there was not a real bed for any of them in the barn and maybe when visitors came to see the baby, she may have laid him in there rather than on the floor to allow people to see him while she stood close by. Maybe she even just laid him down there while she tried to figure out how to construct a bed for the family? Or to use it as a changing table? Regardless, there is not a chance that Mary would have left the Baby Jesus to sleep in a feeding trough. Sure she wrapped him in swaddling cloths but then she picked him up and held him close and snuggled into bed with him asleep in her arms, safe, warm and loved.