Soaking hay can cut sugar, but it may also wash out nutrients: full analysis

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Hay soaking remains a practical strategy for lowering sugar intake in horses at risk for equine metabolic syndrome and laminitis, but the tradeoff is clearer than ever: it can remove useful nutrients along with the sugars. That’s the core takeaway from The Horse’s discussion of the issue, backed by University of Minnesota Extension guidance showing that soaking hay for 15 to 60 minutes lowers water-soluble carbohydrates, potassium, and dust, while longer soaking increases nutrient and dry matter losses. (extension.umn.edu)

The practice has become common in horses with laminitis, insulin dysregulation, PSSM, HYPP, and some respiratory conditions because forage is often the biggest source of nonstructural carbohydrates in the ration. University of Minnesota Extension says complete rations should generally stay below 12% NSC for horses with laminitis and below 10% for horses with PSSM, and notes that many grass hays start above those thresholds. In its hay-soaking data, both orchardgrass hays tested above 12% NSC before soaking, then dropped into roughly the 10% to 12% range after 15 to 30 minutes. (extension.umn.edu)

That said, not every hay benefits equally from soaking. In the Minnesota data, both alfalfa hays were already below 10% NSC before soaking, suggesting they may not have needed treatment for sugar reduction in the first place. Extension specialists also report that crude protein did not materially change with soaking in their work, but magnesium and phosphorus declined across hay types, and long soaking periods created increasingly abnormal calcium-to-phosphorus ratios. After 12 hours of soaking, phosphorus deficiency was observed for a 500-kilogram horse in light work, illustrating why “more soaking” isn’t automatically better. (extension.umn.edu)

Another practical issue is dry matter loss. As hay sits in water longer, horses may consume fewer actual nutrients unless the ration is adjusted upward to compensate. University of Minnesota warns that failing to account for dry matter loss can contribute to unwanted weight loss and low-forage behaviors, including wood chewing and cribbing. The same guidance recommends feeding soaked hay immediately to reduce mold risk and disposing of soak water where horses cannot access it. (extension.umn.edu)

Outside experts broadly align with that middle-ground view. Cornell University’s equine clinicians say that if hay quality is unknown, soaking for 30 minutes before feeding can reduce water-soluble carbohydrates by as much as 50%. Kentucky Equine Research has similarly summarized research showing that 15 to 60 minutes of soaking can produce meaningful nutrient losses, while 12-hour soaking can remove 45% to 65% of some nutrients and may alter the calcium-to-phosphorus ratio enough to justify phosphorus supplementation. (vet.cornell.edu)

Why it matters: For veterinary professionals, this is less a yes-or-no question than a ration-design problem. Horses with EMS, insulin dysregulation, chronic laminitis, or related endocrine disease often need lower-NSC forage, but soaking should be targeted to a diagnosed need and paired with forage analysis whenever possible. The bigger clinical point is that soaking can improve carbohydrate safety while simultaneously making the forage less nutritionally complete, especially if pet parents soak for long periods or use it as a substitute for testing hay and balancing the full diet. (extension.umn.edu)

That nuance also matters for communication. Pet parents may hear that soaking “removes sugar” and assume it’s broadly beneficial, when in fact some hays, especially lower-NSC alfalfa, may not need soaking at all. Others may over-soak in an effort to make hay safer, increasing phosphorus loss and reducing dry matter intake. For practices managing metabolic horses, the most useful advice may be to start with a hay test, define the target NSC range, and then decide whether soaking, forage substitution, mineral balancing, or a combination of all three is the best next step. (extension.umn.edu)

What to watch: Watch for more research that links specific forage nutrient profiles to insulin responses in insulin-dysregulated horses, as well as continued clinical guidance on when soaking is sufficient and when veterinarians should move to a different forage or supplementation strategy. (scholars.uky.edu)