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Understanding fructans

Ever wonder why all that beautiful spring grass can be a problem for your horse and why spring grass seems to be a greater cause of laminitis than summer grass?  After all isn’t grass referred to Dr Green, why is it sometimes the devil in disguise?

There are several factors that make spring grass risky but perhaps the main one for cool season grasses is a type of carbohydrate called fructan a form of complex sugar.  Unlike other simple sugars that are digested and absorbed in the small intestine, fructans, like structural carbohydrates (hemicelluloses, cellulose etc), rely on microbial fermentation in the horse’s hindgut.  However unlike the structural carbohydrates they are fermented very easily.

Fermentation of carbohydrate of all types by the microbial population results in the release of substances called volatile fatty acids (VFA’s).  These volatile fatty acids, most commonly acetic acid, propionic acid and butyric acid, pass through the lining of the cecum and colon into the blood stream where they are transported throughout the body and metabolized.  For example, propionic acid is precursor to glucose, acetic acid may be converted to acetyl CoA a precursor of fat.  In fact for horses fed an all forage diet the volatile fatty acids are their main source of energy.

So what’s the problem with fructan?

When rapidly fermented carbohydrates reach the hindgut the rate at which the VFA’s are produced exceeds the rate at which they are passively transported to the blood stream, resulting in the environment becoming more acidic. In turn this stimulates lactic acid synthesizing bacteria which prefer a more acidic environment.  They in turn utilize the available carbohydrates and create lactic acid which is more acidic than the VFA’s.  This whole cycle results in a condition known as acidosis that changes the environment in the horse’s hindgut.  Lactate utilizing bacteria start to proliferate and convert the lactic acid to VFA’s but they do this more slowly than the synthesizers produce the lactic acid.

What results is an environment that is not favorable for the pH neutral loving bacteria that are necessary for a healthy hindgut.  These bacteria may start to die off and the horse’s ability to utilize forage may be decreased.  This same scenario can be triggered when large grain meals are fed and soluble sugar and starch reach the hindgut undigested.  In this instance you may notice that your horse goes off feed including hay.  To prevent the risk of this happening when feeding grain limit the grain fed in one meal to less than 5lbs of grain for an 1100lb horse.

The die-off of bacteria and acidification of the hindgut may lead to diarrhea, colic as well as laminitis.  The cells that line the cecum and colon are not protected by mucus and as a result are sensitive to damage from an acidic environment.  This can result in erosion, inflammation and ulceration of the epithelia.  In turn bacteria can colonize these injured sites and leak into the blood stream.  When this happens in cattle the bacteria can result in liver abcesses and arthritis as well as other conditions.  In both cattle and horses laminitis can occur and in cattle with rumen acidosis there are reports of increased rates of sole abcesses.

Horses that are carefully transitioned to high fructan pasture are less likely to suffer the negative consequences as their hindguts have time to adapt to higher levels of fructan intake.  This means a slow introduction, building up from very short periods, to an hour or two, to several hours at a time before being granted full access.  Use of grazing muzzles may be necessary for some horses especially if gradual introduction is hard to schedule.  For some horses these pastures will never be safe no matter how carefully introduced, they will need to be maintained on a dirt lot and fed hay.

When is the best time of day to allow your horses access to pasture?

That depends on several factors.  First you need to know a little bit about what types of grasses are in your pasture, cool or warm season, so that you can better judge how these plants may be metabolizing and thus where in the plant sugars may be at any given time. Next you need to know a little about plant metabolism and how sugars and starch are created.

Grasses photosynthesize in response to sunlight.  During the cooler months this causes cool season grasses to create fructan which is stored for use over night when the plant utilizes the fructan as an energy source.  In the hot summer months, warm season grasses will accumulate high levels of starch.

Generally speaking sugar and starch contents of grasses will be higher in late afternoon on a sunny day because of all the photosynthesis therefore making the morning a better grazing option.  However the problem in early spring can be the cool night temperatures.  Cool season grasses shut down their metabolism when the temperature drops below about 40 degrees.  This means that fructans built up during the day are not removed over night.  If horses are turned out on these pastures in the early morning after low over night temperatures, they are being given access to grass that is potentially still high in fructans.

Several days of bright sunlight and cold nights can result in grass that is potentially very dangerous especially to sensitive horses i.e. those that are obese, have a history of laminitis, or are insulin resistant.  For these horses it is likely best to keep them off these pastures all together until night time temperatures remain above 40 degrees.  Once night temperatures are staying above 40 degrees fructan levels will be lowest in the morning, after the plant has utilized stores from the previous day and before it can create more.  If you want to leave your horse out for longer periods, choose days that are overcast and cloudy where photosynthesis is reduced.

In addition to carefully controlling access to such pastures you can help support your horse’s transition through the use of the hindgut buffer Equi-Shure.  This buffer is encapsulated to insure it reaches the hindgut, and has been scientifically proven to help maintain the correct pH in the hindgut, reducing the occurrence of acidosis.  It therefore helps to prevent metabolic issues that result from the over consumption of rich grass.  While the use of Equi-Shure does not mean that you can get away with lax management it can be a good form of additional insurance.  Equi-Shure may be purchased from and using the Champion code CT001 at checkout will grant you a 10% discount.

If you have questions about how to manage your horses on spring pasture be sure to post them in the comments below.  Do you have a story about grazing spring pasture that others could learn from or clever ways of managing your horses on pasture?  Be sure to share them in the comments too!

Grazing spring pasture

Creative Commons License
Understanding fructans by Clair Thunes PhD of Summit Equine Nutrition LLC is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.

Published: Mar 28, 2012
Last Modified: 
June 2, 2024 @ 12:04 am

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