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  • Writer's pictureCoastal Equine

Carbohydrates in Grass – Effects on Behaviour & Performance

Updated: Sep 8, 2019

Originally published on

The Processes of Grass that Create the Sugar Energy

The primary source of feed for most horses is pasture. To understand the horse’s digestion of grass, we have to start with understanding what is happening in the grass. Grass grows by way of a process called photosynthesis and to do this it needs sunlight, warm temperatures, also moisture and carbon dioxide from the air (yes really that gas that many think is so bad for the world!). In the presence of chlorophyll (the green colour) the plant converts those factors into nutrients that create growth above and below the ground and also the development of seed. In winter, the cooler temperatures slow down this process but when spring comes with its warmth, extra sunlight and rainy days, the processing increases and as a result these nutrients which are starch and fructans (sugar) are produced more actively. These are the carbohydrates of pasture. New Zealand pasture is an important part of business in this country, so a lot of development has gone on to create grasses that will create good milk and meat quickly and effectively. That makes much of the grass available to horses very effective in the photosynthesis and therefore high in these carbohydrates.

The issue with the elevated behaviour reactions of horses to grass growth, particularly in Spring, is due to the higher sugar level – fructans. What happens in Spring is not just that grass growth becomes more active, but also the fact that as the mornings are cooler, when the sun is up and photosynthesis starts the starch is still a bit slow as it needs heat. The fructans are up and going and as the growth hasn’t started up (also needs more warmth) the plant stores the sugar and so the stem has a high level. As the day warms up both starch and sugars are increasing but more in balance and they are being used up in the growing process. When night comes the process stops – neither sugar nor starch is produced – and it has been mainly used up in a warm day to grow the stems.

The Effect on the Behaviour of the Horse

Horses do get affected by the higher fructans as they have difficulty digesting these sugars which often pass undigested into the hindgut where they cause hindgut acidosis. This causes discomfort, even pain. So their behaviour changes, although actual responses will vary as horses are all different, but they can before a little hyper -active, spooky, naughty. They may seem tense , touchy and girthy and may even buck. It is mainly the pain or discomfort from the unprocessed feed in the hindgut that causes the biggest reactions.

The Solutions to Help the Horse Become Relaxed Again

It is not the solution to overfeed “calming” products or toxin binders. It is definitely not the solution to starve the horse of grass as this is it’s natural feed and is the most balanced and suitable feed source for a horse.

The grass gets more balanced as Spring moves into Summer and also the horse becomes accustomed to the better pasture. Note fructans can be high in hay, depending on when it is cut, and it can stay easily stored in the hay stems. However it is water soluble and so soaking or washing the hay will reduce the levels of it. While it is ideal to have pasture sown with species more suitable for horses, very few horse owners can do that. So the horses that are susceptible to reacting badly to these fructans need to be kept off the pasture when the sugar is high, so graze them at night, bring them inside or off the grass in the very early morning (a pen maybe) and give them soaked hay instead. As Spring progresses into Summer, gradually let them out earlier – starting evening and then late afternoon – until they can adjust to being out all the time. Remember Horses do need sunlight to create vitamin D. Another solution is to assist horses with the digestion of these sugars and starches. Scientific tests have shown horses can be assisted with their digestion by giving enzymes called alpha amylase and beta glucanase (Richards, Choct et Al).

That is why we created Vetpro Digest-Rite – it contains those enzymes as well as prebiotics called mannan oligosaccharides (MOS) to enhance the gut flora and improve efficient absorption, rice bran with gamma oryzanol and a silicated oxide toxin binder. This unique combination has clearly shown to improve the “Spring behaviour” of so many horses and assist with the variable issues relating to digestion of carbohydrates – whether from grasses or grain ingestion. Grains provide starches and sugars, often to a much higher degree. The issues within the gut are similar – they can also pass though the foregut without digestion and absorption and therefore create acidosis in the hindgut. Again the active ingredients of Vetpro Digest-Rite will assist – the Performance variety is balanced towards assisting the carbohydrate digestion of grain and the Sport variety is balanced towards horses mainly on pasture.

The Toxin Myth

Don’t be misled into “the horse is behaving badly because the grass has toxins” myth! It is particularly the fructans, but also the starches that are the main cause of the Springtime dances. Toxin binders are the latest trend product not required by horses on normal pasture fed fresh feed. A horse that is suffering from ingested mycotoxins becomes sick and shows signs of ill health, not signs of extra energy etc. These toxin binder products were designed primarily for pigs, poultry and cattle. A toxin binder will bind fungi (called mycotoxins) present in mouldy feeds such as grains, but also poorly stored hay etc. Horses that ingest mouldy feed or toxic plants, or are sometimes susceptible to the black seed heads of paspalum, do benefit from a toxin binder. As stated these horses are sick and appear so, importantly they need the services of a veterinarian.

The most well known occurrence of a toxin binder in horses is when they are grazed on endophyte protected rye grass. This is a type of grass used predominately for cattle pasture and the endophyte is a fungi that is deliberately present as it prevents the stem being eaten by beetles, weevils and other bugs and so debilitates the quality of the pasture. This endophyte can release neurotoxins and it is mainly the lolitremB that is harmful to susceptible horses. It causes a condition known as staggers and tends to happen in the Autumn when the grass is short and the animal grazes the low stem. However many modern pastures are being sown with endophyte rye that does not release lolitremB. Normal pasture and any grass most of the year, does not release toxins that cause negative behaviour patterns.

Other Problems from Grass Digestion

Horses that are overweight, sometimes of a chunky body type, are more vulnerable to problems from high levels of carbohydrates and may develop grass laminitis. Again it originates from the horses inability to digest high levels of sugars in the fore-gut and so the undigested feed moves through to the hindgut and that’s where the problem lies. In order to digest in that part of the gut (which doesn’t have the right enzymes) the system issues forth lots of lactic acid. Unfortunately this excess lactic acid kills off good bacteria and as they die they give off a toxin, which then passes into the bloodstream and moves through the fine laminae of the feet, causing the problem called laminitis (founder). A more drastic locking up is required, the weight must absolutely be reduced and again feeding both the enzymes mentioned above in Vetpro Digest- Rite and the oligosaccharides can reduce the negative effects of the founder. Animals with this issue should be presented to a veterinarian for diagnosis and treatment.

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