The NRC tables list minimum daily requirements for many nutrients based on weight, age, reporductive status and work level. The tables are available at the Equi-Analytical website by selecting "Nutrient Requirement Tables" from the "Putting Results to Work" menu.
Enter your horse's body weight (the breed selection option roughly corresponds to expected body weights for that breed) then find the row that matches your horse's class and work level.
For example, let's look at the requirements for an 1102 lb mature horse in light work. His NRC requirements would be
- Dry Matter Intake (at 1.67% of body weight) - 18.5 lbs
- Energy - 20.5 Mcal
- Protein - 820 grams
- Calcium - 25 grams
- Phosphorus - 17.8 grams (Ca:P 1.4:1)
- Magnesium - 9.4 grams
- Potassium - 31 grams
- Sodium - 25 grams
- Iron - 335 mg
- Zinc - 335 mg
- Copper - 84 mg
- Manganese - 335 mg
- Iodine, Selenium and Cobalt - 0.8 mg
- Vitamin A - 22,500 IU
- Vitamin D - 2,510
- Vitamin E - 669 IU
These are "Minimum Daily Requirements" - similar to the human "MDR", they represent the amounts needed to prevent disease, not what is needed for optimal health and performance. More recent research indicates the requirements for many nutrients may be as much as 150% or more of the 1989 NRC recommendations.
Trace mineral and vitamin ranges suggested by KER are:
- Iron - 280-400 mg
- Zinc - 280-500 mg
- Copper - 70-150 mg
- Manganese - 280-500 mg
- Iodine - 0.7 to 2mg
- Selenium - 0.7 to 3 mg
- Cobalt - (no recommendation)
- Vitamin A - β-carotene 500mg (equivalent to 30,000 IU vitamin A activity)
- Vitamin D - only if receiving inadequate sun exposure
- Vitamin E - 2,000 - 4,000 IU
A good quality grass hay will provide most if not all of the protein, energy and most major mineral (calcium, phosphorus, potassium) needs except for magnesium and sodium, and most will provide suficient to excess iron.
Copper, zinc, iodine and selenium will need to be supplemented. Hay quickly loses it's vitamin E content and hay stored longer than 6 months will begin losing it's vitamin A content. A healthy mature horse will synthesize it's own B-vitamins (including biotin) and only requires vitamin D if deprived of sun exposure.
At the very least, a horse should be supplemented with the minimum levels of copper, zinc, iodine, selenium and vitamin E, with loose salt added. Hay analysis can provide a guideline to determine if higher levels of supplementation should be considered and if major minerals need adjustment.