Grass Sugars & Laminitis

With spring around the corner and the longer evenings creeping in most of us welcome spring, but for those of us watching out for laminitis spring can be a worrying time.

Pasture changes and increased availability of turnout create questions as to just how much sugar from grass a horse will be eating.

Let’s take a look at what grass sugar really is and what variation can be expected….

Sugar in Grass

Grass 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. This is why daylight hours and the presence or absence of shaded areas in a paddock plays a big part in the sugar value of your pasture.

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 but growth is slow 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. Fibre is also a source of carbohydrate in plants and an essential part of the horse’s daily diet. As fibre must be provided in adequate quantity for good digestive function and health, restricting forage intake to restrict sugar intake should be done carefully, with the focus on management practices that reduce sugar intake whilst still meeting fibre needs.

How does fructan intake link to laminitis?

Fructan is proven to induce laminitis when given in a large dose. Fructans are not thought to be digested by enzymes in the foregut, which means the majority of fructan will reach the hindgut where it causes changes in bacterial populations. Fructan can increase the presence of lactic acid producing bacteria, which lowers pH of the hindgut, triggering a cascade of events that lead to compromised blood flow.

This is why feeding digestive supplements to support a healthy and balanced profile of bacteria in the hindgut is recommended as part of managing horses at risk of laminitis. Using biotics to create stability helps increase resilience to dietary challenges.

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.

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 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.

How much grass can my horse eat in a day?

Intake of forages is generally averaged at 2.5% of bodyweight per day on a dry matter basis. However, the range on intakes seen is reported as 1.5% up to 5.2% of bodyweight. The range in appetite seen plays a part in understanding why some horses and ponies will get laminitis when grazing the same paddocks whilst others do not.

Where fructan levels are high in pasture and intake rate is also high it is easy for horses to consume significantly more fructan, leading to hypersinsulinemia, as well as an overload of fructan into the hindgut, which can trigger an episode of laminitis.

Restricting time at pasture is an important part of managing intake, however it is worth noting that horses and ponies can adapt their grazing behaviour, grazing intensely when only given access for a limited number of hours. Grazing behaviour is also not a fixed pattern, horses typically consume more in the first 3-4 hours of grazing and then intake rate slows.

Managing pasture and horses prone to laminitis

Conditions that encourage growth of pasture will reduce fructan levels as the sugars produced by photosynthesis are used for growing rather than being converted to fructans.

Keeping pastures grazed, watered and nourished through looking at soil health encourages good growth.

As WSC tends to be higher in the plant stems grazing muzzles are an effective way of reducing total intake and restricting intake to tops of leaves where levels are somewhat lower.

Morning grazing is recommended and ideally within paddocks that are shaded. When temperatures are low in the morning grazing should be withheld or restricted.

Where pasture intake or access is restricted, it is important to provide another source of dietary fibre. Dried forages, whether hay or haylage, are an excellent source of fibre but can be surprisingly high in WSC and should be analysed to confirm the level present especially when feeding a horse with Equine Metabolic Syndrome (EMS) or laminitis.

Considerations for a balanced diet

Restricting pasture intake and also regulating dried forage intake to control for WSC or manage weight gain is a common and needed practice for many horses and ponies. When reducing intake, it is important to remember that other nutrients are also reduced, in part by restriction on intake but also through soaking of forage, a common method to lower WSC. Sugar is not the only nutrient affected by soaking.

Whilst hard feeds might not be an option it is important to provide a source of vitamins and minerals. Supplements providing a daily serving of nutrients are typically fed at low levels and are safe to use for horses with EMS and laminitis.