Fructan index Topical fructan content of grass

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What is the Fructan Index?

Fructan is a substance that can cause laminitis . Fructan is produced by grass, to an extent that depends on the weather conditions.

The fructan index is compiled on the basis of the current weather information. This makes it easy to see if there is a risk of a high fructan content, so you can adjust the grazing time and the duration of grazing.

This page is exclusively about the fructan index. For more information about fructan itself and why it is dangerous for horses, we strongly recommend that you consult the page on fructan . You can then make better use of the information provided by the fructan index.

The card

The map gives an indication of the possible amount of fructan in the grass. The forecast is made on the basis of the temperature and the amount of sunshine. This does not take into account factors such as the type of grass, the availability of nutrients and water.


Use the card with common sense! When conditions are very unfavorable for grass growing, such as persistent drought or lack of nutrients, the fructan content may be high, even though the fructan index predicts from the weather data that the amount of fructan is low.

About the data

The places in the table have been chosen because of their geographical location and because they have an airport where weather conditions are continuously measured. Choose the nearest place, if you live somewhere in between, just look at both places to see which weather type most closely matches your own observation. The difference will not be great enough to cause a dramatic change in the risk factor.
The weather is the type of weather measured at the time shown in the adjacent column. The measurements are carried out by the meteorological departments of airports and have a high reliability. Only the temperature and the amount of sunshine are needed to determine the fructan accumulation, so these are the only data we will show here. For a more extensive weather report you can go to the various online weather stations.
The time displayed is the time when the weather conditions were actually measured by the meteo station. If the time deviates from the current time, this means that no new measurement data were available (server not available, or no new measurement performed, or a technical malfunction, etc.).
The trend indicates whether the amount of fructan is increasing or decreasing. With a lot of sun the trend will be "increasing", one day after fructan accumulation at night usually "decreasing", but this is highly dependent on the temperature and the amount of sunshine.
The risk can take four values: low, moderate, high, very high. The risk depends on the fructan content calculated by the computer model. The four possible values are related to the amount of fructan accumulated. When the risk is low, all horses should be able to graze, provided that no other factors (persistent drought, under-fertilization) increase the fructan content. When the risk is very high, this means that according to the computer model, the fructan content has risen very high. Without a doubt, this is not the most favorable time to let your horse out to pasture. The other values are in between, and it depends a bit on the horse what you do with them. In a horse with recurrent episodes of laminitis, it is better to limit grazing at any value that rises above low, while most horses can still graze fine at an average value.

The algorithm

The algorithm used is based on a continuous fructan consumption (depending on the temperature) and a fructan production (depending on the amount of sunshine, corrected for time and cloudiness). These two effects are added together and a net fructan consumption or fructan accumulation results. This number (negative or otherwise) is added to the existing fructan index. The weather situation is measured and the index is updated every hour.

Fructan consumption

We assume a fructan consumption that continues day and night and is only subject to the ambient temperature.

  • There is no fructan consumption below 5 degrees.
  • When the temperature is higher than 5 degrees, fructan is consumed at 1 unit per hour.
  • When the temperature is higher than 10 degrees, fructan is consumed at 2 units per hour.
  • When the temperature is higher than 15 degrees, fructan is consumed at 3 units per hour.

Fructan accumulation through photosynthesis

To calculate the fructan accumulation we assume that the grass starts to produce fructan as soon as sunlight is available. Sunlight depends on the time of day and the degree of cloudiness.

  • With heavy clouds, a fructan production of 1 unit per hour is assumed.
  • With light clouds, a fructan production of 2 units per hour is assumed.
  • With uncovered skies, a fructan production of 3 units per hour is assumed.
  • More than 4 hours after sunrise and more than 4 hours before sunset, the value is increased by 1 unit per hour.

Fructan accumulation due to frost

It applies that a fructan accumulation takes place as soon as the temperature falls below 5 degrees, this production takes place day and night.

  • At temperatures below 5 degrees, a fructan production of 2 units per hour is assumed.

Frequently Asked Questions

How accurate is the fructan index?

The fructan index provides a guideline only. The exact fructan content depends, among other things, on factors that cannot be measured with the computer, such as the type of grass, the soil type, the availability of nutrients and the like. You must always assess the risks correctly yourself.

The fructan index is not intended to provide a scientifically sound representation of the exact amount of fructan in the grass. The purpose of this index is to give a rough approximation of the probability of a high or low fructan content. The "units per hour" are imaginary values with which the computer model calculates, but which have no relation to an existing measure.

Nevertheless, the various variables that play a role in the build-up or breakdown of the fructan have been taken into account. We assume a growth, and thus consumption, of the grass that is temperature-dependent. We also take into account the anti-freeze effect at low temperatures. The amount of sunshine, on the other hand, determines the amount of fructan that is produced. The various units have been chosen so that they indicate a trend and risk factor that corresponds to situations documented on the Internet.

Can my place of residence be included in the table?

For the fructan index we depend on certain weather information, such as the coverage of the clouds. These data are measured hour by hour by airports. We are therefore dependent for our information on the presence of an airport in the relevant place. Furthermore, the fructan index is not an exact value but more of a rough approximation. If it has frozen at night in Groningen and the sun shines abundantly during the day, you can reasonably assume that the situation in Friesland is not completely different. The measuring points in the table give a reasonable picture of the overall situation, and you have to come up with the rest yourself. Considerations are of course the degree to which the local weather deviates from the nearest measuring point, the sensitivity of your horses to fructan, the type of grass, fertilization, etc. An extra measuring point would not change that situation.

How is it possible that the index for one place in the table differs significantly from the other places?

The weather data depends on airports. The cloud cover is determined at better airports by a meteorologist who looks outside and makes an estimate of the cloud cover. Smaller airports often use automated equipment. There it can happen that in a dense cloud cover there is just a hole in the cloud above the sensor, which then cheerfully reports that it is sunny. Or vice versa. And sometimes there is a malfunction and the last measurements are repeated while the current situation has changed. Again, it appears that the fructan index is a guideline, but that you should always use your own judgment.

In the old version of the fructan index, the fructan value was expressed in a number. Why is that not being done anymore?

The number used did not express a unit but was an imaginary value of the calculation model used. The number suggested a precision that is not there. Nevertheless, people started to make decisions based on this value. The value is now no longer expressed as a number but in a color gradient. That is indeed a bit more vague, but the fructan index itself is also somewhat "vague" so it approximates reality much better. The fructan index is "vague" because besides the degree of cloudiness (which in itself is a vague unit) all kinds of other vague factors play a role, such as soil type, grass type, fertilization, height of the grass, etc. The fructan index is therefore a vague guideline that is primarily intended to be educational.

The fructan index on your own website

Do you want to place the fructan index on your own website? Which can! And it's free too.


The sun rises for nothing. What's behind this?
Easy. We just want it to be known that laminitis is caused not so much by the protein content as by a high fructan content. Many horses still get laminitis every year, despite the well-meaning efforts that owners take to put their horses on a "protein-poor pasture". By providing this information, we hope that it will now become known more quickly that you can save many more horses from laminitis with other measures.

We therefore do not expect anything in return. The only requirement we have is that you show the fructan index in its entirety and leave it intact.

How does it work?

The fructan index is automatically retrieved from our server using the code below. It does not cost you any data traffic, the only data traffic runs from our server to the visitor of your website. The fructan index will contact our server every 10 minutes to check for new data.

Build in

To build the fructan index into your website, copy the code below from the white window. After this you open the HTM or HTML page on which you want to place the fructan index with a text editor such as Notepad or Notepad . Then paste the code where you want the fructan index and that's it: your page now has a professional looking fructan index !