There is a new type of fescue that is said to be endophyte-free now and that may be worth considering. Some breeders switch to alfalfa or timothy three months before the mare is due to foal. Consult with feed and seed suppliers before planning or confirming your nutritional program. Breed only healthy, quality, mature miniature horse stock. Of course, wood chips may be cleaner and some people say that hay or straw can cause damage to the eyes as well.
Straw covers a good deal more ground, but mares often eat the straw and can colic.
If nothing else is available, newspapers might be an option to provide cleanliness and warmth. Never use ground mulch that contains walnut for bedding because it is said to cause a horse to founder. If shredded mulch or sawdust is a dark color, it would probably be safer to assume that it could have walnut in the mixture and choose another bedding. Please bookmark this page and check back often for updates. Kristie Gooding, a miniature horse trainer and breeder who is also a graduate of Virginia Tech University with a BS Degree in Animal Science has written a very helpful article on Weaning Foals that will appear at this site soon.