Soaking Hay: How Much Sugar is Actually Removed?

Grasses and hays high in water-soluble carbohydrates (WSC) can spell disaster for horses with laminitis or insulin resistance (IR). Some veterinarians and nutritionists suggest soaking hay to reduce the amount of WSC in the hay (because water-soluble means these simple sugars dissolve in water), but how much WSC content does soaking actually reduce? According to one team of researchers, it varies depending on how long the hay is submerged.

High WSC levels markedly affect blood-insulin responses in horses and often cause an exaggerated response in laminitic or IR horses. Exaggerated insulin responses can lead to potentially life-threatening bouts of laminitis.

Led by Annette Longland, BSc, PhD, DIC, of Equine and Livestock Nutrition Services in Wales, U.K., a group of researchers recently set out to test the effects of soaking on the WSC and crude protein (CP, to see how much protein was leached during hay soaking) of nine different hays from England and Wales.

The research team completely submerged two kilograms of the mixed species meadow or ryegrass hays either compacted in the flakes or shaken loose of the flake in large plastic tubs filled with 24 liters of 8°C (46°F) tap water. Hays were soaked for 20-minute, 40-minute, three-hour, and 16-hour periods. The researchers then dried the hays in an oven before analyzing them chemically.

As it turns out, soaking hay in water does reduce the WSC, which are comprised mostly of fructans and the simple sugars glucose, fructose, and sucrose, but "there was great variation between individual hays in the amounts of WSC leached," the team reported.

Key findings in the study included:

  • Soaking hay for 20 minutes resulted in the lowest WSC reduction (5%), while soaking hay for 16 hours resulted in the highest WSC reduction (27%);
  • There was no correlation between original WSC content and percentage of WSC reduction for any soaking time period;
  • The effects of soaking on CP varied some, but were not significant; and
  • There was no significant difference in dry matter or WSC content between soaking hay in flakes or shaken loose.

"For owners of laminitic horses, get the hay tested for WSC ... content--preferably after soaking it--so you know exactly how much your hay contains," Longland recommends. "Otherwise, if hay is tested before it is soaked, use soaking as an added safeguard if necessary."

The study "Effects of soaking on the water-soluble carbohydrate and crude protein content of hay" was published in June 2011 in Veterinary Record. It can be viewed online.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.

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