Spring Grass and Horses: NSC Levels, Laminitis Risk & Grazing Management | Equine Science Matters™

After a wetter winter than usual, the arrival of spring sunshine is a welcome relief for horse owners. However, the same conditions that bring lush green fields also create one of the highest-risk periods of the year for horses prone to metabolic problems or laminitis. 

In warm, damp and sunny weather, spring grasses can accumulate high levels of non-structural carbohydrates, otherwise known as NSCs. NSCs found in grass can be split into:  

• Sugars - fructose, sucrose and glucose 
• Starches – long, complex chains of linked sugar molecules 
• Fructans - chains of fructose 

NSC levels will vary due to environmental and soil conditions, and the stage of plant growth. NSCs are produced through photosynthesis- the process by which plants use sunlight energy to produce sugars. This can only occur during daylight hours and is then used to fuel the growth of the plants overnight. Usually, NSC levels are at their highest at 3-4 pm, having accumulated throughout the day, and are lowest early in the morning. However, the use of these NSC’s to fuel growth can only occur when the weather is warm enough. If it has been a very sunny day followed by a cold night (lower than 5 degrees Celsius), the plant is unable to grow and use up the NSC’s, so they accumulate in the leaves to be consumed by our horses the next morning.  

Sugars

Sugars are relatively small molecules and are quickly and easily absorbed in the small intestine. While this means they are highly unlikely to cause an issue in relation to the delicate balance of the gut microbiota, as they are absorbed before reaching the hind gut and caecum, which houses the microbiome, it does mean that there would be a corresponding increase in blood sugar levels that would be unhelpful for horses and ponies with metabolic issues. 

Starch

Starch needs to be broken down into its constituent sugars to be absorbed. This is done by enzymes in the small intestine, and the resultant sugars are then absorbed in the same way as above. Since both starches and sugars are absorbed as sugar in the small intestine, these two forms of carbohydrate are often talked about together. 

Fructans

Fructans are, like starch, composed of long chains of sugar molecules linked together. Unlike starch, fructan is made of lots of fructose molecules linked together, and horses lack the enzyme to separate these molecules. Rather than being broken down and absorbed in the small intestine, they travel through to the hind gut and are fermented by the gut microbiota. Rapid fermentation of fructans disrupts the delicate balance of the gut microbiome, providing more favourable conditions for the less helpful bacteria and hindering the good bacteria. Lactic acid is produced as a by-product of fermentation, which causes the pH of the hind gut to drop, potentially compromising the hind gut as a whole.  

Young spring grass is likely to contain high levels of NSCs, and contains less fibre than older grass, which makes it very easily palatable, and the horse is likely to eat a lot! Consuming a high number of NSCs, especially if the digestive system is not used to it, can lead to many issues, including upsetting the delicate balance of gut flora, which can result in colic or play a role in the development of laminitis. In addition to this, due to the high palatability of the grass, good doers are likely to put on weight. Spring grass can be a particular problem for those who have suffered from laminitis previously, horses with PPID (Cushing’s disease) and EMS, good doers, and those who have gone from a predominantly hay diet onto grass, so these horses may need special management when the spring grass flushes. 

Even if your horse is not predisposed to laminitis, make any changes to the diet slowly. If your horse has been on limited grazing all winter, make the change to being on lush pasture gradual. If necessary, restrict grazing, using muzzles, strip graze, or only turn your horse out for a few hours a day until they are used to the grass in their diet. 

SPRING GRAZING CHECK LIST: 

• Slowly introduce your horse to spring grazing 
• Monitor your horse’s weight carefully 
• Consider pre- and probiotics, which will support the good bacteria in the hind gut 

Be particularly careful with horses/ponies predisposed to laminitis, including horses with Cushing’s disease (PPID) and IR and EMS. 

If the temperature is below 5˚C at night, you may want to consider an alternative option to grass turnout (such as turning out in a ménage or bare paddock). On bright, sunny days, when the temperature is warm, consider turning out on grass for a couple of hours in the morning, when NSC levels in grass are lower. Wearing a muzzle during this time may also be recommended. Monitor your horse closely for early signs of laminitis. It is a common misconception that only overweight native ponies are affected - in reality, laminitis can occur in horses of any breed, age, or body condition, particularly during periods of rapid grass growth.