Roughage is the high-fiber plant material — hay, pasture grass, straw, and similar forages — that forms the nutritional and digestive foundation of a horse’s diet. Horses are hindgut fermenters with a digestive system evolved for continuous consumption of fibrous plant material; the cecum and large colon depend on a steady supply of roughage to maintain microbial populations and normal gut motility. A minimum of 1 to 1.5 percent of body weight in roughage per day (roughly 10 to 15 pounds for a 1,000-pound horse) is the standard threshold below which colic risk increases measurably.
The primary roughage sources are grass hay (timothy, orchard grass, Bermuda), legume hay (alfalfa, clover), and managed pasture. Legume hays are higher in protein and calcium than grass hays; their caloric density makes them suitable for performance horses and lactating mares but potentially too rich for easy keepers. Straw provides fiber with very low nutritional value and is sometimes fed as a dry-matter supplement for horses on restricted rations.
Forage quality is assessed by dry matter, crude protein, digestible energy, calcium-to-phosphorus ratio, and non-structural carbohydrate content. Horses with metabolic conditions such as equine metabolic syndrome or laminitis require roughage with low non-structural carbohydrates; soaking hay reduces water-soluble carbohydrates when tested forage exceeds the threshold. In the context of a cost-effective feeding plan, roughage sourced locally or purchased in bulk represents the most economical nutritional base.
Further Reading: Wikipedia’s overview of forage as an animal feed category covers hay types, nutritional composition, and the role of fiber in herbivore digestion. The Wikipedia article on equine colic explains why insufficient roughage intake is a primary risk factor for digestive obstruction and displacement.