Identifying insulinemic responses of ID horses offered varying levels of NSC and meal-sizes.

This study tested whether post-meal insulin spikes in insulin-dysregulated horses are driven more by the feed’s carbohydrate percentage or by the actual grams of nonstructural carbohydrate (NSC) given per kilogram of body weight in a small meal. It found that once the per-meal NSC dose reached about 0.11–0.12 g/kg BW, insulin rose markedly in insulin-dysregulated horses regardless of the feed’s NSC percentage, though responses varied widely between individuals.

What the researchers wanted to find out

• Whether augmented insulin responses (AIR) in insulin-dysregulated (ID) horses are determined by:
  • The percentage of NSC in a feed (starch + water-soluble carbohydrate), or
  • The absolute amount of NSC delivered per meal, scaled to body weight (grams NSC per kg BW per meal).
• How small pelleted meals with varying NSC content and per-meal NSC loads affect post-prandial insulin in ID versus non-insulin-dysregulated (NID) horses.

Why this matters

• Insulin dysregulation is a major risk factor for laminitis; managing dietary carbohydrate is central to care.
• Owners and clinicians often focus on feed labels (% NSC), but the physiological trigger for insulin release may be the per-meal NSC dose relative to body weight.
• Clarifying dose versus percent NSC helps design safer feeding strategies, especially when using small, test-like meals or concentrates.

Study design at a glance

• Horses:
  • ID: n = 7
  • NID: n = 8
• Feeds (pelleted), spanning a wide NSC range:
  • A: 6.8% NSC (low)
  • B: 14.9% NSC (moderate-low)
  • C: 35.5% NSC (moderate-high)
  • D: 44.6% NSC (high)
• Per-meal NSC doses targeted (g NSC/kg body weight):
  • Low: 0.06
  • Mid: 0.11–0.12
  • High: 0.17–0.18
• Meal size:
  • Small meals on a dry matter basis (~1 g feed/kg BW), adjusted to hit the target NSC dose using feeds with different % NSC.
• Design:
  • Randomized Latin square across two phases to rotate horses through feed–dose combinations and control for horse and period effects.
• Outcomes:
  • Insulin at 60 minutes post-meal (T60).
  • Incremental area under the insulin curve (IAUCi) across the sampling window.
  • Delta insulin (change from baseline).

Key results

• Across all feeds and doses, ID horses had markedly higher insulin responses than NID horses:
  • IAUCi (mean ± SD): ID 3223.1 ± 3229.5 vs NID 907.2 ± 976.4 IU/mL·min (p < 0.0001).
  • T60 insulin (µIU/mL): ID 43.4 ± 48.8 vs NID 12.6 ± 14.6 (p < 0.0001).
  • Delta insulin (µIU/mL): ID 20.9 ± 41.7 vs NID 6.2 ± 11.4 (p < 0.0001).
• Within ID horses, higher per-meal NSC dose drove higher T60 insulin regardless of % NSC:
  • Phase 1:
    • Feed A (6.8% NSC): T60 was higher at 0.17 g/kg vs 0.06 and 0.11 g/kg (p = 0.02).
    • Feed B (14.9% NSC): T60 was higher at 0.11 and 0.17 g/kg vs 0.06 g/kg (p = 0.002).
  • Phase 2:
    • Feed D (44.6% NSC): T60 was higher at 0.18 g/kg vs 0.06 and 0.12 g/kg (p = 0.008).
• Threshold-like behavior:
  • Augmented post-prandial insulin in ID horses consistently appeared at per-meal NSC doses ≥0.11–0.12 g/kg BW.
  • This pattern held independent of the feed’s % NSC.
• Between-horse variability:
  • Large standard deviations indicate considerable individual variation, supporting horse-by-horse monitoring.
• NID horses:
  • Much smaller insulin responses across feeds and doses; no evidence of the same dose-sensitive augmentation seen in ID horses.

How to interpret these findings

• Per-meal NSC load (g NSC per kg BW) is the primary driver of post-prandial insulin spikes in ID horses during small meals.
• A low-% NSC feed does not guarantee a low insulin response if the meal size is large enough to deliver ≥0.11–0.12 g NSC/kg BW.
• Conversely, a higher-% NSC feed can be tolerated if the per-meal NSC grams are kept below the threshold—by feeding a sufficiently small meal.
• The 60-minute time point (T60) captured the dose effect well and aligned with larger overall responses (IAUCi), indicating a clinically relevant window for post-prandial assessment.

Practical takeaways and calculations for feeding ID horses

• Actionable per-meal target:
  • Aim to keep each meal below ~0.10 g NSC/kg BW (i.e., under the 0.11–0.12 g/kg threshold identified in this study).
• How to calculate:
  • g NSC per meal = (% NSC as a decimal) × (meal size in grams of dry matter).
  • g NSC/kg BW per meal = (g NSC per meal) ÷ (body weight in kg).
• Examples for a 500-kg horse (approximate):
  • Threshold dose: 0.11–0.12 g/kg ≈ 55–60 g NSC per meal.
  • 10% NSC feed: 55–60 g NSC corresponds to a 550–600 g meal.
  • 5% NSC forage: 55–60 g NSC corresponds to a 1.1–1.2 kg meal.
  • 20% NSC feed: 55–60 g NSC corresponds to a 275–300 g meal.
  • 40% NSC feed: 55–60 g NSC corresponds to a 140–150 g meal.
• Feeding strategy implications:
  • Divide daily intake into more, smaller meals to limit NSC per meal.
  • Choose low-NSC forages as the diet base; use concentrates sparingly and in very small amounts if needed.
  • If concentrates are required, precisely weigh meals and compute per-meal NSC grams rather than relying on % NSC alone.
  • Monitor individual horses: repeat post-prandial insulin testing or use oral sugar tests to gauge personal thresholds.

Strengths and limitations

• Strengths:
  • Wide NSC range across feeds allowed separation of dose versus percent effects.
  • Latin square design reduced confounding by horse and period.
  • Use of both point (T60) and integrated (IAUCi) insulin metrics.
• Limitations:
  • Small sample sizes, especially in the ID group, and large inter-individual variability.
  • Small pelleted meals may not fully reflect real-world mixed meals or forage-only contexts.
  • Focus on short post-prandial window; other time points or repeated daily dosing effects were not detailed.

Clinical and management implications

• When managing ID horses, calculate and cap the per-meal NSC dose, not just the feed’s % NSC.
• Set a conservative per-meal limit below 0.11 g/kg BW, then titrate while monitoring insulin where practical.
• Because responses vary widely, individualized plans and periodic testing are recommended to minimize laminitis risk.

Future directions

• Define more precise per-meal NSC thresholds across broader horse populations and management settings.
• Examine interactions with fiber type, fat inclusion, and meal frequency on insulin dynamics.
• Extend to forage-based meals and mixed rations to enhance field applicability.