Gypsy, the Equine Encyclopedia, has something to say about the nutrients horses need and how much they need. Like all shetlands, she is always watching, listening and learning.
Water: the average equine needs 5-10 gallons per day.
Protein: should be 8 to 15% of a horse’s daily diet.
Minerals: 2 – 3% of a horse’s diet.
Vitamins: 1% of a horse’s dietary needs.
Energy: Energy is not actually a nutrient. However, there are many energy-producing nutrients including carbohydrates, fat, starch, sugar and fiber. These should make up 80-90% of a horse’s daily nutrition.