Comparison of a colorimetric and a high-performance liquid chromatography method for the determination of fructan in pasture grasses for horses

BACKGROUND

Pasture (fresh or conserved as hay/haylage) forms the basis of most equid diets and contains varying amounts (0 to ≥ 200 g kg⁻¹ dry matter (DM) or more) of fructans. Over-consumption of fructan is associated with the onset of laminitis in equids, an agonizing condition that may necessitate euthanasia. To enable appropriate dietary management of animals susceptible to laminitis, it is essential that fructans can be properly quantified in fresh and conserved pasture. For research purposes, fructans are frequently quantified by high-performance liquid chromatography (HPLC), but these methods are costly for routine screening. However, an inexpensive colorimetric method for measuring fructans in human foods is commercially available. The aim here was to determine the suitability of the commercially available colorimetric method for determining the fructan content of pasture grasses for horses.

RESULTS

Pasture grasses (Phleum pretense, Festuca rubra, Dactylis glomerata, Lolium perenne) managed for grazing (sampled from April to November) and a further set managed for conservation (sampled in July) were analysed for fructan content by HPLC and the colorimetric technique. HPLC values ranged from 83 to 299 g fructan kg⁻¹ DM (mean 154); corresponding colorimetric values were 5-238 g fructan kg⁻¹ DM (mean 82). Discrepancies in values between the two methods varied with time of sampling and plant species. Comparison of selected samples before and after incubation with the fructan hydrolases used in the colorimetric method revealed incomplete fructan hydrolysis from the pasture grasses, resulting in underestimates of their fructan content.

CONCLUSION

The colorimetric technique was not a reliable substitute for HPLC to quantify the fructan content of pasture grasses.