Grass Sugars in Winter

Winter grazing may look poor in quality compared to spring grazing to the naked eye but nutritionally speaking winter grazing can still pack a punch when it comes to fructans. Temperature is one of three key factors that affect fructan content in pasture, meaning cold days and frosty paddocks require caution.

Grass Sugars

Sugar is naturally occurring in green plants. During photosynthesis grass ‘fixes’ atmospheric carbon dioxide in the presence of light, resulting in the production of simple sugars.

When plants produce more sugar than they need for growth or development they convert the sugar into storage carbohydrates. For grasses the storage carbohydrate form is fructan, which when consumed in quantity triggers an insulin response, which can lead to laminitis.

There is no ‘off-switch’ for fructan production, or self-limiting mechanisms, which means fructan production continues even if levels stored with the plant are already high. When conditions are ideal for photosynthesis, such as bright sunny days, but growth is slow due to low temperatures, the amount of fructan can quickly accumulate.

Fructan levels vary during a 24 hour period, being lowest in the morning, reaching maximum levels in the afternoon, and then slowly declining overnight.

Grass will contain both simple sugars and fructans, which when added together create what is known as the Water Soluble Carbohydrate (WSC) fraction of the total carbohydrate value of the plant.

For horses with EMS or laminitis management of WSC from forages and NSC (non structural carbohydrates) from feeds is essential.

How does the environment affect WSC level of pasture?

There are several factors that influence WSC level and variation in level is very high. WSC of a given grass species can easily range from 95g up to 560g per kilogram of dry matter. Fructan within this ranging from 32g up to 439g per kilogram of dry matter. WSC levels follow a seasonal pattern, however variation is high and assessing your pasture on a day to day basis is recommended as weather conditions are the driving factor.

Temperature has a big effect on the level of fructan found. Higher levels are found when temperatures are lower, between 5 and 10 degrees Celsius. Lower values are found when temperatures are in the range of 15 to 25 degrees Celsius.

Shading is also influential as it reduces light exposure. Areas that are consistently shaded have been noted to have half the levels of areas that are unshaded.

Rainfall or rather lack of it can also increase fructan levels. Periods of drought reduce growth but do not stop photosynthesis.

Planning for cold days

When the weather gets cold consider if paddock time is best for your horse. Morning grazing will result in less WSC intake than afternoon grazing. If the paddock is open and without shade keep in mind WSC levels will be higher as shading plays an important role in controlling WSC levels.

When paddock time isn’t possible remember to increase provision of dried forages to ensure fibre and dry matter requirements are met. As pasture is also a source of water for horses be mindful of fluid intake if having to restrict or remove grazing. Additional fluids from feedstuffs or use of electrolytes is recommended to ensure fluid intake is maintained.