06/18/2025
๐ฑ ๐๐ซ๐๐ฌ๐ฌ ๐ข๐ฌ ๐๐จ๐ฆ๐ฉ๐ฅ๐๐ฑ โ ๐๐ง๐ ๐ฌ๐จ ๐ข๐ฌ ๐ ๐ซ๐๐ณ๐ข๐ง๐ ๐ฆ๐๐ญ๐๐๐จ๐ฅ๐ข๐ ๐ก๐จ๐ซ๐ฌ๐๐ฌ ๐ด
After a lively discussion in the comments on my recent post about NSCs (nonstructural carbohydrate) and pasture height, I wanted to follow up with a deeper look at the many factors that influence pasture safety, especially for sugar-sensitive horses.
One of the biggest misconceptions I see is the belief that thereโs a universally โsafeโ time or type of grass for all horses with metabolic issues. While NSC concentrations can sometimes be lower, that doesnโt automatically make the pasture safe. Even reduced levels can exceed what sensitive horses can tolerate, because safety depends on more than just the numbers.
And hereโs the challenge: thereโs no consistent way to predict it. NSCs are highly variable, even on the same pasture, within the same day. Below are just a few of the factors that can influence these fluctuations in pasture NSC.
๐
๐๐ข๐ฆ๐ ๐จ๐ ๐๐๐ฒ:
During daylight hours, photosynthesis creates NSCs faster than they can be used. However, after sunset, respiration uses up the stored sugars. As a result, NSCs can accumulate throughout the day, being the lowest around sunrise and the highest near sunset.
๐ McIntosh, 2007
๐ค๏ธ ๐๐ฎ๐ง๐ฅ๐ข๐ ๐ก๐ญ (๐๐จ๐ฅ๐๐ซ ๐๐๐๐ข๐๐ญ๐ข๐จ๐ง):
Beyond just the time of day, the amount of sunlight matters. On cloudy days, NSC accumulation can be lower due to reduced solar radiation. So, weather impacts sugar levels tooโnot just the clock.
๐ McIntosh, 2007
๐ฑ ๐๐ซ๐จ๐ฐ๐ญ๐ก ๐๐๐ญ๐:
NSCs fuel plant growth. So, when grass is actively growing, it uses up its stored sugars. Fast-growing grass (like freshly mowed, fertilized, or well-watered pasture) tends to have lower NSCs. But stressed, short grass (whether from drought, heat, or overgrazing) may not be able to use up these NSCs as efficiently.
๐ Siciliano et al., 2017
๐พ ๐๐๐ญ๐ฎ๐ซ๐ข๐ญ๐ฒ:
This oneโs tricky. Generally, as grasses mature, their NSC concentrations decrease due to dilution by fiber. But some mature forages still hold high NSC levels. Also, horses grazing taller grass tend to take larger bites, which can increase total sugar intake, even if the percentage is lower. This means maturity is an unreliable indicator of pasture NSC.
๐ Edouard et al., 2009
๐ทโ๏ธ ๐๐๐๐ฌ๐จ๐ง:
Spring grass is often highest in NSCs, triggering strong glucose and insulin responses. Mowing during this period may help reduce risk. In fall, first frosts can spike NSC levels as low temperatures below 40ยฐF (4.4ยฐC) slow or stop sugar metabolism in plants, leading to buildup.
๐ McIntosh, 2007; Siciliano et al., 2017
๐ ๐
๐จ๐ซ๐๐ ๐ ๐๐ฒ๐ฉ๐:
Different forage species store carbohydrates differently. Specifically, warm-season grasses and legumes (such as alfalfa) utilize a self-limiting carbohydrate storage mechanism while cool-season grasses can store as much as they want!
๐ DeBoer et al., 2018
๐ด ๐๐ง๐๐ข๐ฏ๐ข๐๐ฎ๐๐ฅ ๐๐จ๐ซ๐ฌ๐:
Many factors related to the horse itself can influence how they respond to NSCs - things like diet, age, body condition, breed, genetics, and exercise. Science gives us a strong foundation, but every horse is an individual with its own tolerance levels and triggers. Thatโs why blanket statements donโt work. Itโs essential to work with a veterinarian or a qualified equine nutritionist to build a plan tailored to your horse.
๐ Pratt et al., 2006; Bamford et al., 2014; Rapson et al., 2018; Pratt-Phillips, 2024
๐ ๐๐ง๐ ๐ฅ๐๐ญโ๐ฌ ๐ง๐จ๐ญ ๐๐จ๐ซ๐ ๐๐ญ
Healthy horses without metabolic concerns are generally well-equipped to handle grazing, especially when pasture is managed thoughtfully. Their bodies regulate insulin and glucose effectively, and grazing supports natural behavior, movement, and mental health.
๐ฌ ๐๐จ ๐ฐ๐ก๐๐ญโ๐ฌ ๐ญ๐ก๐ ๐ฌ๐จ๐ฅ๐ฎ๐ญ๐ข๐จ๐ง?
๐ Know your horse. Know your pasture. Test when you can.
๐ Use tools like grazing muzzles, dry lots, and turnout timing strategically, not just based on a chart.
๐ Be flexible and smart. What was safe last week or even yesterday, might not be today.
๐ ๐๐จ๐ญ๐ญ๐จ๐ฆ ๐ฅ๐ข๐ง๐:: Grazing for metabolic horses isnโt straightforward, itโs an ongoing conversation between science, observation, and the horse in front of you. NSC levels are influenced by multiple, overlapping factors that canโt be reliably predicted. While the safest option is to avoid grazing altogether, some horses have done well with carefully managed, responsive plans tailored to their forage, their physiology, and their environment.
There is still a LOT we have to learn. What would you like to see reaearch evaluste next?
Cheers,
Dr. DeBoer
๐ผ๐ฃ๐ ๐ ๐๐๐ซ๐ ๐ ๐ฅ๐ค๐จ๐ฉ ๐๐ง๐ค๐ข ๐ผ๐ฅ๐ง๐๐ก ๐ฉ๐๐๐ฉ ๐๐๐ซ๐๐จ ๐๐ฃ๐ฉ๐ค ๐ฉ๐๐๐จ๐ ๐ง๐๐จ๐๐๐ง๐๐ ๐ฅ๐ง๐ค๐๐๐๐ฉ๐จ ๐ข๐ค๐ง๐ ๐๐ฃ ๐๐๐ฅ๐ฉ๐ ๐๐ ๐ฎ๐ค๐ช ๐ฌ๐๐ฃ๐ฉ ๐ฉ๐ค ๐๐๐๐๐ ๐ฉ๐๐๐ฉ ๐ค๐ช๐ฉ!
McIntosh BJ. Circadian and seasonal variation in pasture nonstructural carbohydrates and the physiological response of grazing horses.
Siciliano PD, Gill JC, Bowman MA. Effect of sward height on pasture nonstructural carbohydrate concentrations and blood glucose/insulin profiles in grazing horses. Journal of Equine Veterinary Science. 2017 Oct 1;57:29-34.
Edouard N, Fleurance G, Dumont B, Baumont R, Duncan P. Does sward height affect feeding patch choice and voluntary intake in horses?. Applied Animal Behaviour Science. 2009 Jul 1;119(3-4):219-28.
DeBoer ML, Hathaway MR, Kuhle KJ, Weber PS, Reiter AS, Sheaffer CC, Wells MS, Martinson KL. Glucose and insulin response of horses grazing alfalfa, perennial cool-season grass, and teff across seasons. Journal of equine veterinary science. 2018 Sep 1;68:33-8.
Pratt SE, Geor RJ, McCutcheon LJ. Effects of dietary energy source and physical conditioning on insulin sensitivity and glucose tolerance in Standardbred horses. Equine veterinary journal. 2006 Aug;38(S36):579-84.
Bamford NJ, Potter SJ, Harris PA, Bailey SR. Breed differences in insulin sensitivity and insulinemic responses to oral glucose in horses and ponies of moderate body condition score. Domestic animal endocrinology. 2014 Apr 1;47:101-7.
Pratt-Phillips S. Effect of Exercise Conditioning on Countering the Effects of Obesity and Insulin Resistance in HorsesโA Review. Animals. 2024 Feb 26;14(5):727.
Rapson JL, Schott HC, Nielsen BD, McCutcheon LJ, Harris PA, Geor RJ. Effects of age and diet on glucose and insulin dynamics in the horse. Equine Veterinary Journal. 2018 Sep;50(5):690-6.
