14/06/2025
🌱 𝐓𝐚𝐥𝐥 𝐓𝐚𝐥𝐞𝐬 𝐀𝐛𝐨𝐮𝐭 𝐒𝐡𝐨𝐫𝐭 𝐆𝐫𝐚𝐬𝐬 - 𝐄𝐯𝐚𝐥𝐮𝐚𝐭𝐢𝐧𝐠 𝐭𝐡𝐞 𝐑𝐨𝐥𝐞 𝐨𝐟 𝐆𝐫𝐚𝐬𝐬 𝐇𝐞𝐢𝐠𝐡𝐭 & 𝐍𝐒𝐂 𝐋𝐞𝐯𝐞𝐥𝐬 🐴
I have seen some images and posts circulating lately regarding the ideal grass height to reduce ‘sugar’ intake in horses. The common recommendation is that short grass will have the highest sugars compared to taller grasses. But is this really the case?
📖 𝐋𝐞𝐭’𝐬 𝐟𝐢𝐫𝐬𝐭 𝐫𝐞𝐯𝐢𝐞𝐰 𝐭𝐡𝐞𝐬𝐞 𝐭𝐞𝐫𝐦𝐬 𝐚𝐧𝐝 𝐩𝐫𝐨𝐜𝐞𝐬𝐬𝐞𝐬 𝐚𝐧𝐝 𝐰𝐡𝐲 𝐭𝐡𝐞𝐲 𝐚𝐫𝐞 𝐢𝐦𝐩𝐨𝐫𝐭𝐚𝐧𝐭:
In plants such as grasses, simple sugars (often grouped with starch and fructans and termed nonstructural carbohydrates or NSCs) are produced via photosynthesis. This class of carbohydrate is an important source of energy for the horse and they are digested and absorbed in the foregut, leading to an increase in blood glucose and insulin. As a result, high levels of NSCs in the diet can be an issue for horses with metabolic concerns, specifically related to insulin dysregulation which may be observed in horses diagnosed with equine metabolic syndrome (EMS), Cushing’s (PPID), and laminitis/founder.
The belief that short grass has higher NSCs is due to the fact that grasses tend to store these sugars in the lower base of the stem. As a result, shorter grass is more concentrated in NSC. But is this actually the case – what has the research shown us?
🔬 𝐓𝐡𝐞 𝐫𝐞𝐬𝐞𝐚𝐫𝐜𝐡.
A study performed in New Jersey evaluated cool-season grass pastures and compared short, continuously grazed pasture (2.9 to 4.1 inches/7.3 to 10.5 cm) to a taller, rotationally grazed pasture (5 to 9.5 inches/12.4 to 24.1 cm). This study found that the ‘sugars’ in the grass, as well as the glucose and insulin responses in grazing horses, were the same regardless of grass height. Rather, season and time of day were two important variables capable of altering these carbohydrate concentrations.
📚 Williams et al., 2019
A separate study in North Carolina evaluated horses grazing tall fescue pasture mowed down to 5.9 inches (15 cm) 11 days prior to grazing horses compared to taller grass (11.8 to 15.8 inches/30 to 40 cm). This study found that the shorter, mowed pasture resulted in less simple sugars and a subsequent decrease in the insulin response of grazing horses compared to taller grass.
📚 Siciliano et al., 2017
𝐁𝐮𝐭 𝐰𝐡𝐲 𝐰𝐨𝐮𝐥𝐝 𝐭𝐡𝐢𝐬 𝐛𝐞?
🍃 Short or overgrazed grass may lack sufficient leafy surface to produce and store sugars effectively.
🌱 Under stress, plants may move sugars into the roots—where grazing horses can't reach them.
🌾 Shorter grass that is actively growing is more likely to utilize the NSC to contribute to growth whereas a taller, more mature grass will accumulate and store more NSCs.
🐴 Horses can consume more grass per bite when eating tall grass (Eduoard et al., 2009) which could result in greater sugar intake as well as an increased glucose and insulin response.
𝐒𝐨 𝐰𝐡𝐚𝐭 𝐝𝐨𝐞𝐬 𝐭𝐡𝐢𝐬 𝐦𝐞𝐚𝐧?
These findings suggest that short grass may not be as concerning as we originally thought. With that said, there are a few things to keep in mind:
⚠️ There will always be a risk when allowing sugar-sensitive horses to graze fresh forage due to regular fluctuations in the NSCs in pasture.
✂️ Managing pastures is important, and while shorter grasses may be beneficial, it is important not to overgraze pastures (less than 4 inches).
🧪 The only way to truly know the NSCs in the forage is by sending a sample to a lab for analysis. While this is trickier to do with fresh forage (since it constantly changes), it can create a baseline to guide decisions.
🗺️ There are many factors that may influence these findings so it should not be applied broadly and should be considered within the context of your horses, location, species, and management style.
📌 𝐓𝐡𝐞 𝐭𝐚𝐤𝐞𝐚𝐰𝐚𝐲
Grass height alone is not a reliable measure of pasture safety. For metabolically sensitive horses, effective management—not grass length—is what truly matters.
Cheers,
Dr. DeBoer
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.
Williams CA, Kenny LB, Burk AO. Effects of grazing system, season, and forage carbohydrates on glucose and insulin dynamics of the grazing horse. Journal of animal science. 2019 May 30;97(6):2541-54.
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.
