Drought causes pastures to dry up, weeds to flourish, and horses to get thin without supplemental feeding. But there are other things going on in your fields that you need to know about in order to protect your horses from problems such as laminitis, colic, diarrhea, and toxic weeds. The problem isn’t over when the rains come; conversely, the much-needed, drought-breaking rains can cause additional problems to grazing horses.

One might think that green grass is highest in nutrients and brown grass is lowest. This is true for some nutrients, but not all. When dead grass is rained on, water-soluble nutrients are leached out. But under drought conditions, they remain; your pasture might actually be higher in non-structural carbohydrates, which includes sugars, starch, and fructan.

Most cool-season grasses accumulate sugar and fructan (a type of sugar) under drought stress. When plant growth slows due to lack of water, the balance between photosynthesis that creates sugar, and growth that uses sugar, is lost. Sugar levels rise in intense sunlight, and high sugar levels trigger formation of fructan, which is the storage form of carbohydrate in cool-season grasses. Warm season grasses do not make fructan, preferring starch for carbohydrate storage.

Fructan reserves are like the fat on a hibernating bear: The more fructan plants can accumulate before they go dormant, the more energy reserves they have to sustain them during the drought and allow them to get a competitive advantage when conditions are again favorable for growth. Unfortunately for horses eating these plants, fructans are a known trigger for laminitis in susceptible horses