Differences between starch and sugar
Starch are carbohydrates and they are in high concentrations in cereals, i.e. oats, barley, wheat and rye. In the small intestine starch is rapidly degraded to glucose and absorbed into the blood. When horses eat starch rich concentrates there is a risk that non digested starch reaches the hindgut causing the microflora to produce lactic acid which is a strong acid that can acidify the hindgut environment, read more about this here. Sugars are water-soluble carbohydrates and are found in for example grass and in grass the most common sugars are glucose, fructose, sucrose and fructans.
Table 1 shows examples of amounts of starch and sugar in cereals from table values and in three different grass leys and a lucerne ley which have been used in feeding experiments with horses. The concentration of starch in cereals is much higher than the concentration of sugar in grass. In addition the horse consumes concentrate much faster than it consumes forage.
Studies of the equine hindgut have shown that when horses eat cereal based concentrates the pH in caecum and colon can decrease drastically, which acidifies the environment. One meal of two kg pelleted barley resulted in pH values down to 6.4 in caecum. A cereal based pelleted concentrate given in 1.08 kg/100 kg BW and day resulted in pH values down to 6.2 in caecum and colon, but also lower pH values of down to 5.9 have been measured when feeding large concentrate meals. However, when horses were fed only early harvested forage (grass ley 1, > 1 kg DM/100 kg BW and day) the pH in colon varied between 6.7 – 6.9 and the concentration of lactic acid in the colon was below the detection limit. So early harvested grass with high sugar content does not imply acidification or deterioration of the hindgut environment, on the contrary! However both starch and sugar affects the insulin levels in the blood which is of importance for horses with insulin resistance.
In conclusion sugar from forage and starch from concentrate does not have the same impact on the hindgut environment. Starch rich concentrates impair the hindgut environment after feeding which sugar rich grass does not.
Sara Muhonen, AgrD