Rely on forage tests before and after soaking to decide which type of hay is best for your horse especially with a horse that has laminitis, PSSM, HYPP or COPD.
For these horses NSC, P and mold content are key.
Soaking hay for 15 to 60 minutes is a good way to manage these horses, but only soak hay if your preferred hay isn’t available.
Feed soaked hay right away to avoid mold growth.
Dispose of water in random grassy areas that horses can’t access.
Why soak hay?
Soaking hay in water is a common way to care for horses diagnosed with one of the following.
Polysaccharide Storage Myopathy (PSSM)
Hyperkalemic Periodic Paralysis (HYPP)
Chronic Obstructive Pulmonary Disease (COPD)
Soaking hay for 15 to 60 minutes in water reduces water soluble carbohydrates (WSC), potassium (K) and dust. Each of these elements play a role the diseases mentioned above.
Researchers suggest complete rations (hay, grain and supplements) should contain less than 12 and 10 percent nonstructural carbohydrates (NSC)(starches and sugars in forage) for horses with laminitis and PSSM, respectively.
Reynolds et al. 1997 found that horses with HYPP need complete diets less than 1 percent K.
Moore-Colyer 1996 found that soaking hay for 30 minutes reduced respiratory problems for horses with COPD or heaves.
Does soaking hay remove other nutrients?
We looked at four hay types including:
Budding alfalfa (AB)
Flowering alfalfa (AF)
Vegetative orchardgrass (OV)
Flowering orchardgrass (OF)
Prior to soaking, both alfalfa hays were below 10 percent NSC (Table 1). Thus, this hay didn’t need soaking for horses with PSSM and laminitis. Low NSC is common in alfalfa since legumes store carbohydrates as starch.
Grasses have higher NSC levels because they store their carbohydrates as fructan. Both grass hays had NSC levels above 12 percent. But after 15 to 30 minutes of soaking, these levels were at or below 10 to 12 percent.
Although soaking hay longer further reduced NSC content, we don’t recommend it. All horses need carbohydrates in their diet. High fiber and very low NSC content in hay soaked for greater than 1 hour could reduce palatability and nutrients available in hay soaked longer.
Table 1: NSC1 content in bud (AB) and flowering (AF) alfalfa and vegetative (OV) and flowering (OF) orchardgrass before and after soaking in cold (C) or warm (W) water
|Hay||Pre-soaking||15 min - C||15 min - W||30 min - C||30 min- W||60 min - C||60 min- W||12 hrs - C|
1 non-structural carbohydrates estimated by adding water soluble carbohydrates (WSC) plus starch.
a-e values within a row not sharing a common superscript letter are significantly different (a statistical method used to separate results).
Soaking didn’t affect crude protein content.
Prior research looked at the nutrient availability and quality of rained-on hay fed to steers. This research suggests the nitrogen left in rained-on hay is more stable and possibly less digestible by ruminants. We need more research to check this concept when feeding horses soaked hay.
Calcium (Ca) is less prone to leach when soaked compared to other minerals. It’s leaching appears to depend on hay maturity. The longer the soaking, the more Ca leached from alfalfa bud and vegetative orchardgrass hays. These hays are immature. Soaking didn’t affect Ca leaching in the more mature hays.
Calcium to phosphorus ratio
Soaking reduced magnesium (Mg) and phosphorus (P) levels in all hay types. Longer soaking times lead to greater reductions. Thus, there were high Ca:P ratios in hays soaked for longer times. Ideally, Ca:P ratios should range from 1:1 to 3:1 (up to 6:1) in horse rations.
After 12 hours, Ca:P ratios ranged from 8:1 to 10:1 in alfalfa hays. But grass hays had good Ca:P ratios during all soaking lengths. This is mostly due to lower Ca amounts prior to soaking. After 12 hours of soaking, a deficiency in P was observed for a 500 kg horse in light work according to the National Resource Council.
Alfalfa and orchardgrass need to soak for 60 minutes to reduce K to recommended levels prior to feeding HYPP horses. While soaking reduces K, neither alfalfa or orchardgrass is a good option for HYPP horses. Both of these forages are naturally high in K. Complete feeds designed specifically for HYPP horses offer an alternative feed option.
Soaking decreased dry matter over time. Nutrient loss from soaking can be accounted for by looking at dry matter. Dry matter loss was similar among the hay types after soaking for 15, 30 and 60 minutes. But there was greater dry matter loss after 12 hours of soaking compared to the other soak times.
If you don’t consider dry matter loss, this may lead to unwanted weight loss or poor horse behaviors. These behaviors arise from low levels of forage in the diet and include wood chewing and cribbing. Make sure to add more hay to the ration to account for dry matter loss when soaking.
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Authors: Krishona Martinson, Equine Extension specialist; Marcia Hathaway, professor, College of Food, Agriculture and Natural Resource Sciences; Hans-Joachim Jung, adjunct professor emeritus, College of Food, Agriculture and Natural Resource Sciences; Craig Sheaffer, professor, College of Food, Agriculture and Natural Resource Sciences
Reviewed in 2021