Optimal Grazing for the “Easy Keepers”, Metabolically Sensitive and Founder-Prone Horses: Dr. Marthe Wildsmith

Thank you to Westhills own Dr. Marthe Wildsmith for joining us on the blog today to break down safe and effective grazing! Please reach out to the clinic with any nutrition questions for your horse or for a more detailed consult with Dr. Wildsmith or one of our other veterinarians!

Metabolic and weight-related conditions in horses are an increasing concern among horse owners and equine veterinarians. Horses with insulin resistance (IR), equine metabolic syndrome (EMS), Equine Cushing’s Disease or Pars Pituitary Intermedia Dysfunction (PPID), as well as easy keepers, those with a history of laminitis or founder, or simply just breed sensitive, are all at higher risk of dangerous blood sugar fluctuations and pasture-related laminitis. One of the most effective, non-pharmaceutical strategies for managing these horses involves carefully controlling pasture access—and that’s where timed (restricted) grazing and strip grazing come into play.

Understanding the Challenge

Lush pasture, while natural and appealing, often contains high levels of non-structural carbohydrates (NSCs), particularly in the spring and fall. These sugars can trigger insulin spikes and weight gain, which are dangerous for metabolically sensitive or founder-prone horses.

Horses with high fasting insulin levels (over 300 pmol/L) are at especially high risk for laminitis when turned out on unrestricted pasture. Early detection and management are crucial for prevention. In a crisis, feeding very low NSC hay in a dry lot is recommended. However, if there is no active laminitis, completely removing pasture access isn’t always practical or desirable, especially considering its benefits for mental well-being and digestive health. That’s why targeted grazing management is key.

Time-Restricted Grazing

This approach limits grazing to specific windows each day—for example, during the early morning hours when sugar content in grass is typically lower. For many horses, starting with 30–60 minutes per day and gradually adjusting based on weight and metabolic health allows for safe pasture access without compromising their condition.

Tips for Success:

Monitor grazing times closely and adjust as needed.
Use a grazing muzzle for additional control if appropriate. Grazing muzzles can reduce intake by 50–80%.
Schedule regular veterinary check-ups and, for metabolic horses, insulin-glucose testing.

Strip Grazing

In general, taller, mature grass tends to have lower NSCs, while short, stressed, or rapidly regrowing grass often has higher sugar concentrations. For sensitive horses, the ideal grazing height is 6–8 inches, allowing access to lower-sugar forage while protecting the root system and avoiding overgrazing.

Strip grazing involves sectioning off a smaller portion of the pasture with temporary fencing and moving it incrementally. This provides horses with controlled access to mature grass while limiting the amount of fresh growth available at any given time.

Benefits include:

Controlled NSC intake
Encouragement of steady movement and natural foraging behavior
More even pasture use, reducing overgrazing and regrowth of high-sugar grass

Alberta Summer Pastures: A Seasonal Advantage

In Alberta’s summer months, particularly mid-to-late summer, pasture sugar levels in cool-season grasses—Timothy, Orchardgrass, Brome, Fescue, and Kentucky bluegrass— generally decline as temperatures rise and growth slows, making grazing safer for metabolically sensitive horses.

Remember:

Heat slows growth: As temperatures increase, cool-season grasses photosynthesize less actively, reducing NSC storage.
Species matter: Cool-season grasses typically decline in NSC in hot weather; warm-season grasses like Teff and Buffalo grass may stay higher in sugars.
Environmental stressors: Drought, mowing, frost, or excessive grazing can spike NSC levels even in summer.

Typical NSC Ranges in Summer

Safe threshold for sensitive horses: Less than 10–12% ESC + starch

Average cool season grass NSC in summer is 9-11%
Evening NSC often remains higher than morning by 2-3%, sometimes up to 9%

In Alberta, typical summer pasture NSC on cool season grasses hovers just under or near that safe threshold - around 9-12% but can spike above 12% under stress.

Timed Grazing to Minimize NSC Intake

Early morning grazing is ideal: Grasses use stored NSC overnight for growth, lowering sugar levels by morning.
Avoid late-afternoon grazing: Hot, sunny conditions drive peak NSC levels.
Skip grazing after stress events: Frost, drought, or mowing can cause temporary NSC spikes.

Practical Steps for Alberta Horse Owners

Test your pasture: Summer NSC varies by microclimate—test both early morning and late afternoon to identify safe windows.
Use timed grazing: Limit access to early morning hours (before 10 a.m.) and adjust total grazing time, especially during active growth periods.
Do strip grazing: Control intake further by fencing small paddocks and moving horses daily. This also encourages movement and reduces consumption of young, high-sugar growth.
Avoid high-risk conditions: Hold off grazing after mowing, drought, or frost—even in summer.
Keep hay available: Provide low NSC hay (under 10%) in a slow-feed net when horses are off pasture to prevent hunger-driven binge eating.

The Bottom Line

With careful monitoring and strategic grazing, Alberta summer pastures can be a valuable, low-risk resource for easy keepers, metabolic horses, and those sensitive or prone to laminitis. By timing grazing early in the day, using strip grazing or muzzles, testing pasture sugars, and adjusting turnout based on environmental conditions, horse owners can safely balance the benefits of pasture access with the need for metabolic health.