While we traditionally associate fast-growing, lush grass with springtime, autumn can bring its own “grass flush” too. Changing weather, especially after a dry summer, can result in similar changes to grass structure, sugar levels and even mineral content.
After months of slow or stunted growth, it’s a relief to see green fields again. But when grass starts growing quickly after a dry spell, cold weather, or low nitrogen levels, it can lead to big changes inside the plant. During stressful times (like drought), grasses store energy in the base of the stem or roots. Once the weather improves, those stored sugars known as non-structural carbohydrates (NSCs) move back up into the blades, where your horse can easily eat them.
That means rain after a drought, warm sun after a cold or frosty night, and fertiliser on poor grass can all lead to a higher-than-usual NSC (sugar) content in grass.
Why it matters
This rapid grass growth results in grass that is soft, sweet, and very tempting, so horses often eat a lot, very quickly. Most of the sugars (NSCs) are broken down by enzymes into simple sugars in the small intestine, where they’re absorbed into the bloodstream as energy. For horses that are prone to laminitis or metabolic conditions like EMS, this sudden rush of sugar can be extremely unhelpful. Even for healthy horses, these NSCs (sugars) can cause unwanted weight gain.
When this sudden influx of sugar occurs, it can overwhelm the absorption capacity of the small intestine, meaning that some of these NSCs pass through to the large intestine (the hindgut). Horses also can’t digest one particular sugar, fructan, which always travels to the hindgut.
Once these sugars (NSCs) reach the hindgut, they’re rapidly fermented by bacteria that produce lactic acid. This lowers the pH of the hindgut and upsets the balance of good bacteria. That drop in pH, gas that is produced as the NSCs are fermented, and changes to osmotic potential (water balance) in the hind gut can result in discomfort, free faecal water and diarrhoea.
As a combination of these diet-related factors can contribute to the development of laminitis, owners of susceptible horses and ponies should be particularly careful with access to grass during the autumn months.
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Managing autumn grazing
For horses and ponies that are sensitive or prone to laminitis, autumn can be a risky time. Being strategic about when to turn out can limit the amount of NSCs (sugars) in the grass while your horse is eating it, helping to reduce the risks associated with an autumn flush:
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Avoid turning out on sunny mornings after a cold or frosty night. Sugar levels are often highest then.
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Bring horses in earlier when it’s been a sunny day, as the sunlight increases photosynthesis rates, so NSCs will accumulate throughout the day.
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Restrict grazing on new growth after a drought. This grass is often rich in sugars (NSCs)
Although these steps can help reduce sugar intake while still allowing plenty of access to grass, they are by no means foolproof. Temperature fluctuations, water and nutrient availability, sunlight and the type of grass you have will all affect where and how much NSC a plant has stored, and there is no exact way of checking their levels each day.
Safer options for at-risk horses
If you have horses and ponies with sensitive gastrointestinal systems, metabolic issues, or a tendency to gain weight easily, the safest approach is to limit grass access, just as you might in spring.
You can do this by:
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Using a grazing muzzle
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Strip grazing
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Turning out in a dry lot or grass-free area for part of the day
The takeaway
That lush autumn grass can seem like a welcome relief after the long, dry summer, but it comes with its own set of risks for certain horses and ponies. While keeping a close eye on the weather and temperature fluctuations can give some guidance as to the likely sugar (NSC) content of the grass, the safest option for at-risk horses and ponies is to restrict grazing as we would in spring until we are into the winter.
