Most horse owners of laminitic/ overweight/ EMS or Cushing prone ponies are actively involved in managing grazing and restricting turn out, writes Carol Michael.
This is because grass and hay contain water soluble carbohydrates in the form of simple sugars compromising of sucrose, glucose, fructose and also fructans which may trigger an attack.
Owners may also be aware that sugar content tends to vary depending on the seasons and weather conditions and as such, spend a great deal of time selecting ‘safe’ grazing times to avoid a sugar overload.
Clearly horses are designed to eat and digest grass but are also foragers of shrubs and herbage, a fact that many of us overlook. Many native breeds are also designed to thrive in harsh conditions on inferior pastures.
But in our modern stabled and rugged environment, is it possible to find ‘safer pasture’ or have some kind of accurate way of calculating sugar intake depending on what type of grasses?
With a view to finding safe pasture, Bangor School of Chemistry in Wales has been investigating the sugar content of some of the so-called inferior native species of grass compared to the more modern and most popular grass sown in Britain, which is Perennial Rye and compromises a whopping 86% of grass seed sales.
Since 2005 Perennial Ryegrass has been bred to have a high (80%) content of fructan whatever the weather or other environmental conditions. This makes sense to the dairy farmer who wants a high milk yield in the most economical way without feeding large quantities of hard feed, but makes it hard for horse owners who have been under the impression fructan levels can vary and there may be safer times to graze horses.
The idea behind the development of the high sugar ryegrass varieties was that the rumen bacteria tend to preferentially metabolise the fructan, leaving more amino acids available to travel through to the hind gut to be absorbed by the cow, resulting in better weight gain and better nitrogen use efficiency in the animal, but making this grass type entirely unsuitable for native horses/ponies.
There are two types of laminitis that may result from overgrazing. One is endocrinopathic and the other is alimentary. Endocrinopathic laminitis is the result of a high fructose intake, and alimentary laminitis is the result of an overload of fructans which alter gut microbiota because they cannot be digested by the horse.
Fructose and Fructan are digested in different ways. Fructose is digested in the small intestine and is then transported into the blood in the form of glucose. As it hits the blood stream the body immediately signals a release of insulin to take the glucose out of the blood as glucose is toxic to the vital organs. To protect the vital fight or flight mechanism the horse has a strict policy on glucose control and it is quickly either used or stored. Continuously high levels of glucose equal a continuous release of insulin and the research from Chris Pollitt and Cathy McGowan (2011) revealed that high insulin levels will trigger an attack of laminitis.
Experts appear to be divided in their opinion on how frutans are digested. Some report that fructans are fermented in the hind gut and produce lactic acid and VFA which cause a change in the gut PH . Some researchers are of the opinion they are indigestible to the horse and pass out un-digested, which is why they are often included in the horse’s diet as a prebiotic (oligfructose).
Much of the grassland research in Britain has concentrated on feeding dairy cattle and turf growing for sports facilities and though there are pony pasture types of seed available to buy little has been done to analyse the fructose and fructan content of these indigenous species.
Therefore, the initial project at Bangor University was to analyse the fructose content of a 25 year old variety of Perennial Rye (lolium perenne) compared to the more modern variety to see if the fructose levels had
increased along with the fructans.
At the same time the university also analysed the fructose content of a range of old pasture grass species including Yorkshire Fog, Meadow Fescue, Cocksfoot, Creeping Bent, Red Fescue and several more. This was with the assistance from Ianto Thomas at Ibers, who runs a global seed bank. He provided several validated grass species from his plant collection of over 25,000 original types that are stored on site.
The research project ran from October 2012 until October 2013 and includes seasonal comparisons of sugar content together with a two hourly comparisons of five native grass species and also Perennial Rye.
The first set of results received were quite remarkable, indicating that the fructose content of both the old and new varieties of Perennial Rye were high in fructose, but the new variety is even higher with a 332mg/g fructose content in comparison to 0.52mg/g in Meadow Fescue.
Therefore modern Perennial Ryegrass, which is the most popular type of grass grown in the UK, has the potential to give the laminitic prone pony a double whammy of sugar in the form of fructose and also a high ingested fructan level.
Meadow Fescue is actually 0.52 fructose, 0.26 glucose and 0.19 sucrose whilst the Crested Dogstail is 0.48, 0.23 and 0.13 – too low to show on the chart.
If given the choice of Perennial Rye over Meadow Fescue the horse will inevitably choose the sweeter variety and over indulge on its sweet sugary content, whilst the Meadow Fescue will be far less appealing and the horse will eat slower and will more likely pick at other plants on offer as a healthy alternative!