Recent studies suggest that fructans might be involved in pasture-induced laminitis in horses.
Fructans are storage molecules produced by the grass when it produces more sugars by photosynthesis than are needed for immediate use.
Fructans are poorly digested in the foregut of the horse. If large quantities reach the hindgut they are rapidly fermented by the microorganisms, leading to a cascade of events that may result in laminitis.
In a three year study Jürgen Grässler and Uwe von Borstel, working at the Landwirtschaftskammer in Hannover, Germany, looked at fructan content in the species of grasses that are commonly found in horse pasture. They harvested grass samples every two or three weeks during the growing season. Samples were collected at 11.00 each morning to prevent the results being influenced by time of day.
Dr Grässler presented their findings at the Equine Nutrition Conference held earlier this month in Hannover.
They found that Lolium perrene (Perennial ryegrass) and Lolium multiflora (Italian ryegrass) contain the highest amounts of fructans - an average throughout the year of 5.7% on a dry matter basis. However, they found that the fructan content varied throughout the year, being highest in May and October. The fructan content fell during the summer. They also found a difference between strains of perennial ryegrass. One strain ("Anton") had the highest fructan level of 14.2%DM in autumn 2003 and 13.6% DM in spring the same year.
All other pasture grasses contained low fructan concentrations - on average about 3.5% DM. Again, the highest fructan concentration was found in the first growth in May and in October. The fructan content of the grass was lowest during the summer.
The second part of the study looked at the fructan content of grass mixes that might be used for horse pasture. Grässler and von Borstel found that mixtures with a high proportion of Lolium perrene gave the highest fructan levels . The highest levels were found in pastures containing only Lolium perrene (15.2%). During the growing season the highest fructan content was measured in late June (11.4% DM average) and in October.
Grässler and von Borstel conclude that grass mixes with high amounts of Lolium perrene may contain high fructan concentrations, especially in spring and autumn, and are less suitable for feeding horses predisposed to laminitis.
To minimise the risk of laminitis they suggest that grass mixtures with reduced quantities of Lolium perrene should be used. Pastures with forage grasses such as Alopecurus pratensis (Meadow Foxtail) and Phleum pratense (Timothy) as the main components are suitable to produce low fructan concentrations.
Reference: Fructan content in pasture grass. Jürgen Grässler and Uwe von Borstel. Proceedings Equine Nutrition Conference. Pferdeheilkunde (2005) 21, 75 - 76.