Tool

Hay NSC Calculator

Cites lit reviews 2, 7, 8, 9

Enter the values from your forage test report. The calculator interprets them against PSSM management thresholds and gives you a verdict plus actions. Numbers are interpreted on a dry-matter (DM) basis, which is how Equi-Analytical and Dairy One report by default.

Information only, not veterinary medical advice. Use the result as a conversation starter with your veterinarian, not as a final decision. Severe PSSM cases and horses with concurrent insulin dysregulation may need stricter targets than the defaults.

Enter your forage test values

All values as % of dry matter (DM). Leave blank if your test did not report it.

What the numbers mean

NSC (Non-Structural Carbohydrates). The total of sugars and starch. The single most important number for PSSM management. Standard target: under 10% on dry matter. Some labs report this as a calculated value (NSC = WSC + Starch).

ESC (Ethanol-Soluble Carbohydrates). Simple sugars (mono- and disaccharides) extractable in ethanol. A tighter measure than WSC. For severe PSSM or any horse with insulin dysregulation, watch ESC more closely than WSC.

WSC (Water-Soluble Carbohydrates). Includes ESC plus fructans. Fructans are not directly absorbed in the small intestine but reach the hindgut where they ferment. WSC is more relevant for laminitis risk than for muscle disease specifically.

Starch. Reflects grain content (timothy, orchard grass, alfalfa hays should be low; oat hay or barley hay can be much higher). Starch directly contributes to glycemic response and is a key parameter for PSSM.

What if your hay tests above the threshold?

You have several levers, in order of practicality:

  1. Soak the hay. Soaking grass hay in cold water for 30-60 minutes can reduce WSC by 30-50%, though variability is high[8]. Re-test if you can; do not assume.
  2. Dilute with lower-NSC forage. Mix 50/50 with a tested low-NSC hay. The composite NSC is approximately the average.
  3. Source different hay. Late-cut grass hays (later in the growing season) tend to have lower NSC than early-cut. Mature timothy is typically lower than alfalfa-grass mixes.
  4. Feed less of it. If quality is otherwise good but NSC is borderline, reducing the proportion of hay calories and replacing with low-NSC fiber sources (beet pulp, soybean hulls) can work.

Source thresholds

SeverityNSC ceilingESC ceilingStarch ceiling
Lenient (mild PSSM, light work)12%10%4%
Standard (typical PSSM)10%8%4%
Strict (severe PSSM, insulin dysreg)8%6%2%

Synthesized from lit_review_02 and lit_review_07. Specific thresholds in clinical recommendations may vary; the standard column reflects the most commonly cited targets in the systematic reviews.