The National Organic Program requires that producers establish and maintain livestock living conditions, which accommodate the health and natural behavior of animals, including:
(1) Access to the outdoors, shade, shelter, exercise areas, fresh air, and direct sunlight suitable to the species, its stage of production, the climate, and the environment;
(2) Access to pasture for ruminants;
(3) Appropriate clean, dry bedding (if the bedding is typically consumed by the animal species, it must be organic); and
(4) Shelter designed to allow for:
(i) Natural maintenance, comfort behaviors, and opportunity to exercise;
(ii) Temperature level, ventilation, and air circulation suitable to the species; and
(iii) Reduction of potential for livestock injury.

You can find good information on livestock housing in some Rodale publications at: www.rodaleinstitute.org or by visiting www.attra.ncat.org.