Definition

In horse nutrition, the term sugar refers to ethanol-soluble carbohydrates (ESC) measured in the Equi Feed analysis. These sugars are primarily glucose produced by plants through photosynthesis. In grasses, glucose is stored as fructans in the stem or seed, while in crops it is stored as starch in seeds or roots. Fresh grass does not contain starch. 

Importance

Sugars are rapidly digested by enzymes in the small intestine. However, if sugar intake is excessive, undigested sugars pass into the large intestine, where they are fermented by bacteria. Since the large intestine is adapted mainly for fibre digestion, this shift in bacterial population can lead to serious health issues such as laminitis. Therefore, knowing the sugar content of forage is essential for managing horse health.

Water-Soluble Carbohydrates (WSC)

WSC includes both ESC (simple sugars) and fructans, meaning the WSC content of hay is always higher than the sugar content alone. Soaking hay in water can reduce WSC levels, which is why it is important to know both sugar and WSC values to estimate how much carbohydrate can be removed during soaking.

Fructans

Fructans are complex sugars produced by plants during photosynthesis and stored as an energy reserve. Their concentration increases when plants experience stress, such as:

• Lack of water
• Poor fertilisation
• Low temperatures (below 10°C) combined with high sunlight

Under these conditions, plants accumulate fructans to use later when growth conditions improve. Currently, fructans and WSC are analysed only in hay.

Key considerations

• Monitor sugar and WSC levels in forage to prevent digestive disorders.
• Use hay soaking as a strategy to reduce WSC for horses prone to laminitis.
• Understand plant stress factors that influence fructan accumulation.

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