We do the same as Terri H., bed with a good layer of shavings and then some soft hay on top of that for about a week or two when the foal is stronger! I feel like there is less chance of straw colic that way. For years previously I had used a good clean straw on on top of shavings and while I personally didnt have any trouble, as I always fed a lot of hay to discourage the mares from eating the straw, but my vet told me some minis at the clinic really had some bad colics and one had died, due to ingesting so much straw. So last year I decided to try the shaving with clean soft hay on top, and it worked just fine, the mares munched on the hay, which was a soft timonthy orchardgrass mix, after they finished up their normaly alfalfa orchardgrass mix, but all did well on it.