Cold, sunny days and freezing nights give us some beautiful, frosty mornings, but for owners of horses and ponies who are metabolically challenged, have Cushing’s or very sensitive digestive systems, it can be tricky to manage.
Sunny days increase the rate of photosynthesis - the rate at which the green pigment called chlorophyll in the plant can use sunlight, carbon dioxide and water to create sugars otherwise known as Non-Structural Carbohydrates (NSCs). Increased sunlight increases the quantity of sugars the plant can produce, within reason. In the correct conditions, the grasses can use these sugars to grow, respire and repair themselves.
However, when the temperature drops to below approximately 5°C, the plant’s respiration effectively shuts down. The NSCs accumulated during the day cannot be used for growth and remain stored in the plant, available for horses to consume when they are grazing. Frosty grass or turning horses out in the morning after a cold night can therefore result in a sudden influx of NSCs into the digestive system.
What happens in the intestine?
Normally, sugar and starch are broken down in the stomach and small intestine. Picture the small intestine as a multi-lane motorway. Nutrients are like cars, each colour representing a different type. Sugars, let’s say, are red cars.
Along this motorway are special exits designed just for red cars. When only a few arrive at a time, they easily slip off at the right spots and enter the bloodstream at a manageable pace.
But imagine turning a hungry pony onto high-NSC frosty grass. Suddenly, a huge wave of red cars floods the motorway. The exits clog. Some traffic backs up. And many red cars are forced to continue straight past their intended exits, ending up in completely the wrong place -the hindgut.
For healthy horses, this is still not ideal. But for those with insulin resistance, EMS, or Cushing’s, this sudden flood of sugar entering the bloodstream can be particularly dangerous. When it does, the less-friendly bacteria jump on it quickly. This leads to:
- rapid fermentation
- production of lactic acid
- a drop in hindgut pH
This environment is tough on the helpful microbes and can lead to:
- loose droppings and free faecal water
- excess gas
- discomfort
- behavioural changes
For sensitive horses
For horses with metabolic issues who are likely to struggle with higher NSCs, the following tips may help:
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Limit grazing when the temperature is below 5 degrees, and once the temperature has increased, wait a couple of hours before turning out if possible.
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To reduce the sugar content of hay, it will need to be soaked for longer in cold weather.
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Encourage movement – movement is key to keeping blood sugars under control.
Where loose droppings and free faecal water are the predominant issue, the following ideas may help resolve the problem:
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Again, avoid turnout when the grass is frozen or during early thaw.
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When replacing grazing with hay, remember that hay has a much lower water-holding capacity than grass. Consider replacing part of the hay ration with grass chop to increase the water-holding capacity of the diet.
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Avoid making any sudden dietary changes. When swapping between batches of hay, mix the two batches together to transition gradually.
A sudden onset of loose droppings or free faecal water can also be indicative of a wide range of issues, so while a change to the NSC content of the grass is a likely explanation, these symptoms may warrant a call to your vet.
