Pasture Grass Height & Laminitis Risk in Horses by a Vet – 2025 Guide to Carbs, Mowing & Safe Grazing 🌾🐴

By Dr Duncan Houston, BVSc

Introduction

Managing pasture access is one of the biggest challenges for owners of insulin-resistant horses or those with a history of laminitis. In 2025, new research offers insight into how the height of grass affects non-structural carbohydrate (NSC) levels and ultimately the laminitis risk in grazing horses. While mowing grass may reduce sugar intake slightly, it is not a foolproof strategy for metabolic horses.

The Laminitis–Insulin Connection 🔄

• Laminitis is often triggered by high carbohydrate intake from lush pasture
• Non-structural carbohydrates (NSCs) increase blood glucose
• This leads to an insulin spike—a known laminitis trigger in insulin-dysregulated horses
• Even short grazing sessions on rich grass can trigger an episode

North Carolina State Study: Mowing vs. Grass Height ✂️🌱

Researchers compared horses grazing on tall (12 inch) vs. mowed (6 inch) tall fescue pastures. Here’s what they found:

• Horses ate less when grazing shorter grass
• They still consumed enough forage to meet their basic needs
• Some horses lost weight while grazing the mowed pasture

What This Means

• Shorter grass may help reduce calorie and NSC intake
• However, the difference may not be significant enough for high-risk horses

Important Study Limitations 🧪

• The study used healthy horses with no metabolic issues
• Pasture was tall fescue only—results may not apply to ryegrass, Bermuda, orchardgrass, etc.
• Did not test horses with diagnosed equine metabolic syndrome (EMS) or PPID

Why Grass Still Poses Risk for EMS Horses ⚠️

• Carbohydrates in grass fluctuate by:
  • Time of day – highest in the afternoon
  • Weather – sunny, cold conditions increase NSC content
  • Growth stage – short, stressed grass can be higher in sugar than mature grass
• Mowing grass may not sufficiently reduce these levels for insulin-sensitive horses

Safe Pasture Strategies for Insulin-Resistant Horses 🧠✅

1. Use a Dry Lot

• Best way to avoid grass sugars completely
• Provide low-NSC hay tested below 10%

2. Consider a Grazing Muzzle

• Limits intake while allowing turnout time
• Monitor closely for muzzle rubs and effectiveness

3. Limit Grazing Time

• Turn out in the early morning when NSC levels are lowest
• Still risky for high-risk horses, even with short exposure

4. Test Your Pasture

• Send grass samples to a lab to measure NSC content
• Know what you’re working with before grazing high-risk horses

5. Prioritize Weight Management

• Obesity increases insulin resistance and laminitis risk
• Weight loss = reduced insulin levels and reduced flare-up risk

Case Example: Pony with Recurring Spring Laminitis

1. Overweight Welsh pony turned out on mowed pasture in spring
2. Owner assumed short grass was safer
3. Pony developed mild lameness within 4 days
4. Vet diagnosed subclinical laminitis
5. Pony moved to dry lot, given low-sugar hay and started weight-loss plan
6. Returned to soundness in 2 weeks with no pasture access

FAQs About Grass Height and Sugar in Horses

Q: Is short grass lower in sugar?

A: Not necessarily. Stressed or overgrazed grass can be higher in NSCs than tall, mature grass.

Q: Can mowing prevent laminitis?

A: Mowing may reduce intake, but is not a safe strategy for high-risk or insulin-resistant horses.

Q: What’s safer—hay or grass?

A: Tested low-NSC hay is much safer and more consistent than grazing pasture.

Conclusion

While mowing grass can reduce forage intake and potentially lower sugar levels, it’s not a guaranteed method to prevent laminitis in horses with insulin resistance, metabolic syndrome, or PPID. In 2025, the safest approach remains controlled diets, tested hay, and non-grass turnout areas. Monitor your horse's weight, insulin levels, and hoof health closely throughout the year.

Need help creating a safe grazing plan for your horse? Visit AskAVet.com or download our app 📱 to consult Dr Duncan Houston for laminitis prevention and pasture advice. 🩺🐴