Soaking Hay: Why Reducing Sugar Also Means Losing Nutrients
For horses prone to laminitis, insulin dysregulation, equine metabolic syndrome or other sugar-sensitive conditions, soaking hay has become a widely adopted management tool. The reasoning is straightforward. Hay contains water-soluble carbohydrates, including simple sugars and fructans, which can provoke dangerous insulin spikes in susceptible horses. Immersing hay in water dissolves and removes a portion of these sugars, lowering metabolic risk and making some forages safe to feed. Yet research published across the past decade and, critically, in the past three years, has sharpened understanding of the tradeoffs involved. Soaking does reduce sugar, but it also removes a wider spectrum of nutrients that horses rely on for health, growth and performance.
How Much Sugar Does Soaking Remove?
Recent studies examining soaked forage confirm that soaking hay for 30 to 60 minutes can reduce water-soluble carbohydrates by around 30% to 50%. This reduction often brings many grass hays below the commonly recommended non-structural carbohydrate threshold of 10% to 12% for metabolically sensitive horses. However, results vary with species and maturity. Ryegrass may remain above safe limits even after immersion, while a mature timothy hay may fall well within recommended ranges. The international consensus is clear but nuanced. Soaking helps, but cannot compensate for extremely high sugar hays, and forage analysis remains a valuable tool for precise dietary management.
A more recent review, Understanding Sugar and Nonstructural Carbohydrates in Equine Pasture and Hay (Hathaway and Martinson 2024), reinforces these findings. The authors confirmed that soaking hay for 15 to 60 minutes reliably reduces non-structural carbohydrate concentration, supporting its role as a management tool for horses with insulin dysregulation or laminitic risk. However, the same review underscores that soaking does not selectively remove sugar. Instead, water-soluble minerals and components of the protein fraction are also leached, altering the nutrient profile of the forage in ways that must be accounted for when formulating the ration. The authors caution that owners often underestimate how much nutrient loss occurs, particularly when soaking becomes a long-term daily practice.
Note: It is important to note that no alterations to feed regimes are made without first consulting a qualified equine nutritionist and/or veterinarian, particularly when managing horses with metabolic, orthopaedic or gastrointestinal conditions.
The Hidden Cost: Protein, Minerals and Dry Matter Loss
The wider nutritional implications of soaking have been well documented. A 2021 study published in the Journal of Equine Veterinary Science found that soaking hay for just 15 minutes significantly reduced almost every nutrient measured. Digestible protein was among the most affected components. Although crude protein percentage changed very little, the protein available for absorption in the small intestine declined by approximately 35%. Amino acid availability also decreased, which matters for muscle repair, immune function and hoof quality.
Mineral losses can be equally consequential. Phosphorus and magnesium, both essential for metabolic stability and skeletal health, are highly soluble and were shown to decline substantially during soaking. Potassium, which supports nerve and muscle function, may fall by more than half during extended soaking. Calcium remains comparatively stable, which distorts the calcium to phosphorus ratio. Ratios exceeding 6 to 1 have been recorded after prolonged immersion, potentially impairing mineral absorption and bone strength.
Dry matter loss further complicates the picture. Trials comparing hay before and after immersion demonstrate reductions of 10% to 20% in dry matter after a one hour soak. This means that unless owners increase the quantity of hay offered, horses consuming soaked hay will ingest fewer calories and less fibre. For overweight horses, this can accelerate weight loss. For horses in work, growing horses or those maintaining a healthy body condition score, such inadvertent deficits may lead to muscle loss and reduced overall condition. Research by Argo and colleagues has shown that obese horses fed restricted soaked hay lost weight considerably faster than predicted, largely due to leached nutrients and reduced energy density.
Soaking also affects palatability. With natural sugars removed, some horses become reluctant to eat soaked hay, reducing their intake or seeking alternative fibre sources such as wood or bedding. Monitoring actual forage consumption therefore remains essential.
Feeding Soaked Hay Safely and Responsibly
Despite these challenges, soaking hay remains an important and often essential practice for horses at risk of laminitis or insulin related disorders. The key lies in understanding that soaked hay is not nutritionally equivalent to dry hay. It is lower in energy, lower in available protein and lower in several key minerals. Shorter soaking times generally offer the best compromise between sugar reduction and nutrient retention. A broad spectrum vitamin and mineral balancer is often prudent to replace lost phosphorus, magnesium and trace minerals. Horses in regular work may require additional high quality protein sources to counter the reduction in digestible protein associated with soaking. Where possible, forage analysis before and after soaking provides useful data for tailoring feeding programmes accurately.
Soaking hay remains a valuable strategy in modern equine management, particularly given the rising prevalence of metabolic disorders worldwide. The evolving body of scientific evidence does not diminish its usefulness but clarifies its limitations. By understanding what is removed along with sugar and adjusting the wider diet accordingly, owners and professionals can ensure their horses receive the benefits of reduced sugar intake without compromising long term health or welfare.
Sources:
Argo, C. M., Curtis, G. C., Grove-White, D. and others (2015) Weight loss resistance in the obese pony: Should we be concerned. The Veterinary Journal, 204(2), pp. 208–214.
Bochnia, M., Meyer, H., Reyer, H. and others (2021) Effect of soaking on the nutritional composition of hay for horses. Journal of Equine Veterinary Science, 100, 103600.
Hathaway, M. R. and Martinson, K. L. (2024) Understanding Sugar and Nonstructural Carbohydrates in Equine Pasture and Hay. ResearchGate.
Longland, A. C. and Byrd, B. M. (2022) Changes in the composition of soaked grass hays. Grass and Forage Science, 77(3), pp. 345–356.
Martinson, K. L., Peterson, M. L., Hathaway, M. R. and others (2022) Water soluble carbohydrate leaching in soaked hays. University of Minnesota Equine Extension.
Moore-Colyer, M., Latham, R. and Longland, A. (2020) Changes in microbial contamination of hay following soaking and steaming. Animals, 10(12), 2379.
