Soaking hay for 15 to 30 minutes is enough to significantly reduce water-soluble carbohydrates (WSC) for laminitis-prone horses. Longer soaking times don’t meaningfully improve sugar removal, and they introduce risks like bacterial growth and excessive nutrient loss. Here’s what you need to know to do it right.
Why Soaking Time Matters Less Than You Think
A study testing meadow hay soaked for 15 minutes, 30 minutes, 60 minutes, and 12 hours found that just 15 minutes of soaking at room temperature significantly reduced fructans, WSC, and several minerals. The key finding: longer soaking durations did not enhance the wash-out effect. The sugar that’s going to leach out does so quickly, mostly within the first 15 to 30 minutes.
That said, different hays behave differently. Research testing nine different meadow hays found that only 2 to 9 percent of WSC leached within the first 20 minutes, and the amount lost varied substantially between hays regardless of their starting sugar content. This means you can’t predict exactly how much sugar your specific hay will lose from soaking alone. If your horse is severely laminitis-prone, getting your hay tested before and after soaking gives you a much clearer picture than guessing.
Cold Water vs. Hot Water
Water temperature affects how fast sugars dissolve. Cold water soaking for about 60 minutes and hot water soaking for about 30 minutes both remove a considerable percentage of WSC. If you’re using cold water from a hose or trough, give it the full 30 to 60 minutes. If you have access to hot water, you can cut that time roughly in half. Either way, you don’t need to soak for hours.
The 10% NSC Target
The goal of soaking is to get your hay’s nonstructural carbohydrate (NSC) content below 10% of dry matter. NSC is the combined total of water-soluble carbohydrates and starch, and it’s the number that matters for laminitis management. The American College of Veterinary Internal Medicine recommends keeping NSC below 10% for horses with equine metabolic syndrome, and this threshold is widely used for any horse prone to laminitis.
Soaking alone won’t guarantee you hit that target. If your hay starts at 25% NSC, a 30-minute soak might bring it down to 18%, which is still too high. Starting with low-sugar hay and then soaking it as an extra precaution is a more reliable strategy than relying on soaking to fix high-sugar hay.
What Else Leaves With the Sugar
Sugar isn’t the only thing that washes out. A 30-minute soak reduced potassium levels by about 41% in one study of timothy-alfalfa hay. Potassium loss is actually beneficial for some metabolic horses, since high potassium intake can worsen insulin resistance. Soluble protein also drops after soaking.
Calcium concentration actually increased by about 32% on a dry-matter basis after soaking, not because more calcium appeared, but because so much other material washed away that calcium made up a larger share of what remained. Phosphorus levels stayed the same. This shifts the calcium-to-phosphorus ratio, which may matter if your horse’s overall diet is already calcium-heavy. Overall energy content drops too, since you’re removing digestible carbohydrates. Horses eating soaked hay may need supplemental vitamins and minerals to make up for what’s lost.
Don’t Soak Too Long
Soaking for hours doesn’t pull out more sugar, but it does create hygiene problems. Bacteria, mold, and yeast all multiply in soak water, and the longer hay sits in that water (or sits wet after draining), the worse it gets. Warm weather accelerates the problem. Research on stored soaked hay found that bacterial and fungal counts climbed with both time and temperature after treatment.
The practical rule: soak for 15 to 30 minutes, drain for about 20 minutes, and feed immediately. Don’t prepare soaked hay hours in advance, and don’t let it sit in the sun. If you soak a batch and your horse doesn’t eat it within a reasonable window, discard it rather than risk feeding hay with elevated microbial counts.
Disposing of Soak Water
The leftover water is more polluting than you might expect. It carries a high biological oxygen demand, meaning the dissolved sugars and organic matter consume oxygen as they break down. Dumping it into ponds, streams, or storm drains can harm aquatic life. Spreading it over a large area of grass or gravel, or pouring it onto garden beds, is a better approach. If you’re soaking hay daily, the cumulative volume of effluent adds up, so plan a disposal spot that can absorb it without creating runoff.
Steaming as an Alternative
Commercial hay steamers kill dust, mold spores, and bacteria without the downsides of soaking. Steaming does remove some WSC, but not as much as soaking. If your primary concern is respiratory health and your hay is already low in sugar, steaming may be the better choice. If sugar reduction is the priority, soaking wins. Steaming also produces far less polluting waste water, which matters for daily use over months or years.