Spring grass

Spring is knocking on our door and that lush green grass is starting to emerge.

Spring grass can cause a variety of issues including; colic, diarrhoea, insulin resistance, behavioural problems and laminitis. The grass is worse after a cool night followed by a sunny day because of the sugars and fructans in the grass increase during these conditions which have a negative effect on your horse.

Laminitis: Especially horses that are insulin resistant are at risk of developing laminitis. Therefore, it’s important to work out how you can prevent laminitis. Does your horse or pony have a body condition score of 7 or more on a 0-10 scale? Then talk to your vet about your options to prevent health issues.


Grass growth and sugars

Grass constituents change as the plant grows and even throughout each day. During the day plants and grass use the suns energy to produce sugars through the process of photosynthesis. Therefore the grass will contain more sugar at the end of a sunny day than it did in the morning. At night the grass undergoes the process of respiration where it uses sugars for growth, therefore sugar levels are lowest in the early morning. During winter and early spring, the low night temperatures inhibit the grass’ metabolism, preventing the grass from using its sugars (glucose, sucrose and fructose) for growth. Due to this process, you can appreciate that a warm sunny day followed by a cool frosty night will create the perfect condition for high sugar levels to be maintained until the next day when the grass makes more sugars again, causing the sugar level to spike. This is detrimental to the sugar sensitive horse.


Level of fructans in the grass

Fructan is a nutrient the grass creates and uses for growth. The plant also uses fructans to protect itself against frost. Therefore, it’s prudent to monitor the levels of fructan in the grass when the temperature drops below 5°C. Moreover, when grasses can’t use their sugars for growth, they can convert sugars into fructans to keep as a reserve energy source. During periods of stress (such as dry land, nutrient deficient land, grass grazed very short or when the grass has been trampled) the grass will produce more fructans for survival. Fructans are mostly stored in the stem, while sugars are mostly stored in the leaf of the grass; therefore short grass is packed full of fructan especially when frosty.


Sugar and fructan digestion

The horse digests sugars from the grass in their small intestine. These sugars (glucose) then enter the blood stream which triggers the pancreas to produce insulin. Insulin tells cells to take in glucose from the blood stream through special receptor channels. In horses with insulin resistance, a surge in the blood-glucose elicits an abnormal insulin response, which can cause laminitis.

The horse doesn’t digest fructans, the bacteria in the hind gut do. These bacteria that are part of the normal hind gut flora, they convert fructans into lactate, which in turn serves as an energy source for other bacteria in the hind gut. The bacterial flora of the hind gut adjusts itself to the horse’s diet. However, these adjustments take time, which is why dietary changes always need to be made gradually, ideally over a two-week period. When the grasses change suddenly and the hind gut flora aren’t used to high concentrations of fructans it can cause the hind gut to acidify. This causes the good bacteria to die and release toxins which, just like all nutrients in the gut, can be absorbed into the blood. This, and a high insulin level can cause laminitis. Other consequences of the acidified hind gut are indigestion, colic and diarrhoea.


How much grass does your horse eat?

Grass contains 80-85% water, the remaining components are nutrients for the horse (termed the “dry matter” fraction), these include fibre, sugar, fats, proteins, vitamins and minerals. When horses are on pasture 24/7, they can eat 2% to 3% (sometimes even 5% !!) of their body weight in dry matter every day. A 600 kg horse can eat about 80 kg of grass a day, which equals to 12.5 to 15 kg of dry matter.


The risks of spring grass

Digestive disorders: colic and diarrhoea

When the sugar content in the grass suddenly increases it causes the bacteria in the hindgut to produce a lot of gas. If these gasses are produced too quickly or not passed rapidly, it can cause colic.

“Young”, lush spring grass contains more protein and less fibre, which speeds up digestion and transit time. This can cause diarrhoea.

When the grass is short and growth is slowed during winter, horses can pull out the grassroots as they graze. These roots often have sand attached which the horse ingests. Horses can also ingest sand when they graze on muddy paddocks or drink from puddles in the pasture. It is normal for the horse to ingest tiny amounts of sand, but if this level becomes too high, the sand can accumulate in the intestine. This can be a slow process that happens over years. Nevertheless, when a horse accumulates too much sand in its intestines it can also cause colic and/or diarrhoea.


Insulin resistance (IR), Equine Metabolic Syndrome (EMS) and laminitis

The most common sequelae to high sugar and fructan levels in the grass is laminitis. This is especially important for horses and ponies that have had laminitis in the past or those who suffer from insulin resistance (IR) or equine metabolic syndrome (EMS). IR can be caused by PPID (previously known as Cushing’s disease), EMS or obesity, but can also happen at the end of pregnancy. A horse that has IR has a risk of developing laminitis. Laminitis is a very painful condition of the feet that can lead to founder, a possibly life-threatening disease. 



Horses originate from a natural environment where they had to travel long distances to get to food sources. Their diet consisted of mature grasses, shrubs, bushes and tree bark if sources were low. The pastures that horses graze on today are very lush compared to the diet they evolved to eat and they no longer are required to cover great distances to find it. This has led to a relatively high percentage of horses that are overweight, which has serious negative health effects. It can lead to poor performance and diseases such as IR, EMS and laminitis. Therefore, it is important to do a body condition score (BCS) every 6 weeks (4 weeks in summer) to monitor your horse’s weight. The horse’s weight can be managed by 1) exercise and 2) strip grazing. Mature grasses contain less energy and sugars than short or young grass. However, long grass has the disadvantage that horses can eat more of it, so again it may be better to strip graze your horse. It’s best to restrict their access to grass in the mornings after a cold night (<5°C). If you’d like to reintroduce your horse to grass after being restricted, it can help to feed the horse hay first so that the horse doesn’t gorge itself. However, if your horse suffers from IR the priority will be to get the IR under control. A specifically formulated diet will help to make sure goals are met without the risk of your horse losing weight too quickly, which would make them prone to developing hyperlipaemia (liver disease). If you would like to know more about your horse’s BCS, whether your horse has IR or how to set up a healthy and appropriate diet for your horse, then please contact your vet. 



  • Strip grazing / restricted pasture access / no pasture access for horses that are overweight or are at higher risk of laminitis due to IR, EMS or previous episode of laminitis. Call your vet to discuss management options that best suit your situation.
  • Pay attention to when the levels of sugars and fructans in the grass may be high.
  • Regularly check the Body Condition Score of your horse (every 6 weeks) and keep notes. If you think your horse might be overweight (or underweight) contact your vet to formulate a plan.

If you have any questions about this article or your horse, please contact us.


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