Soaking hay in water is a common strategy used to manage horses diagnosed with laminitis, PSSM, HYPP and COPD. Hay soaking for short durations (15 to 60 minutes in duration) is an acceptable management method for these horses. Soaking hay for longer durations resulted in very low carbohydrate concentrations, high Ca:P ratios, and significant losses in dry matter. Owners should rely on forage analysis as the primary method of determining the appropriate hay for horses.
Soaking hay in water is a common strategy used to manage the nutrition of some diseased horses. Current hay soaking recommendations include soaking hay for 30 minutes in warm or 60 minutes in cold water for removal of water soluble carbohydrates (WSC), potassium (K) and dust (Cottrell et al., 2005). Soaking hay is commonly done to help manage WSC, K and dust intake in horses diagnosed with laminitis, polysaccharide storage myopathy (PSSM), hyperkalemic periodic paralysis (HYPP), and chronic obstructive pulmonary disease (COPD). Researchers have suggested that complete rations (hay, grain and supplements) contain less than 12% nonstructural carbohydrates (NSC) (starches and sugars in the forage) for horses affected with laminitis (Frank, 2009), and and 10% for horses affected with PSSM (Borgia et al., 2009). Reynolds et al. (1997) determined that a complete diet less than 1% K is necessary for rations with horses diagnosed with HYPP, and Moore-Colyer (1996) determined that soaking hay for 30 minutes reduced respiratory problems for horses diagnosed with COPD or heaves.
However, how efficient is hay soaking, and are other nutrients lost during the soaking process? Researchers at the University of Minnesota set out to determine the impact of water temperature and soaking duration on removal of NSC, crude protein (CP), minerals, and DM from alfalfa and orchardgrass hays.
How the Research was Conducted
Four hay types were soaked, including bud stage alfalfa (AB) and flowering alfalfa (AF), and vegetative (OV) and flowering orchardgrass (OF; Table 1). Individual flakes were submerged for 15, 30 and 60 minutes in 6.6 gallons of cold (72°F) and warm (102°F) water, and for 12 hours in cold water (Table 2). A control (non-soaked) sample was also evaluated. Water temperatures were selected by turning on the cold or warm faucets only. Subsamples of entire flakes were submitted for nutrient analysis at a commercial laboratory.
Removal of Nonstructural Carbohydrates
Prior to soaking, both alfalfa hays were below the 10% and 12% NSC levels recommended for horses diagnosed with PSSM and laminitis, respectively, and would not have required soaking (Table 1). This is common for alfalfa, since legumes store their carbohydrates as starch, compared to grasses that shore carbohydrates as fructans (sugars).
The orchardgrass hays were above these recommendations. After soaking for 15 to 30 minutes they were at or below 10% to 12% NSC. Although soaking hay for longer durations did further reduce NSC content, it is not recommended. All horses, even diseased ones, require carbohydrates in their diet. The very low NSC content in hay soaked for greater than 1 hour, combined with increased fiber amounts (fiber components are not water soluble, thus they become more concentrated in soaked hay), brings into question the palatability and availability of nutrients in hay soaked for longer periods of time.
Table 1. Concentrations of non-structural carbohydrates1 in bud (AB) and flowering (AF) alfalfa hay and vegetative (OV) and flowering (OF) orchardgrass hay, before and after soaking in cold (C) or warm (W) water.
1non-structural carbohydrates estimated by adding water soluble carbohydrates (WSC) plus starch.
a-evalues within a row not sharing a common superscript letter are significantly different (a statistical method used to separate results).
Removal of Crude Protein
Crude protein content was not affected by soaking, something other researchers have also observed (Moore-Colyer, 1996; Cottrell et al., 2005). More importantly, previous research looked at the nutrient availability and quality of rained-on hay fed to steers and suggested the nitrogen remaining in rained-on hay is more stable, water-insoluble (Rotz and Muck, 1994), and possibly less digestible by ruminants (Licitra et al, 1996). Additional research is needed to evaluate this concept when feeding soaked hay to horses.
Removal of Minerals
Calcium (Ca) is not as prone to leaching during soaking compared to other minerals, and it appears to be dependent on hay maturity. As soaking duration increased, leaching of Ca increased in alfalfa bud and vegetative orchardgrass hays (immature hays).
However, soaking had no effect on Ca leaching in the more mature hays. Conversely, magnesium (Mg) and phosphorus (P) levels were reduced in all hay types as a result of soaking, with longer soaking durations leading to greater reductions. Because Ca is not as water soluble as P, high Ca:P ratios were observed in hays soaked for longer durations. Ideally, Ca:P ratios should range from 1:1 to 3:1 (up to 6:1) in horse rations (NRC, 2007). After 12 hours, Ca:P ratios ranged from 8:1 to 10:1 in alfalfa hays. However, grass hays had acceptable Ca:P ratios during all soaking lengths, mostly due to lower amount of Ca prior to soaking. After 12 hours of soaking, a deficiency in P was observed for a 500 kg horse in light work (NRC, 2007).
Soaking alfalfa and orchardgrass hay for 60 minutes was necessary to reduce K concentration to near recommend levels prior to feeding horses diagnosed with HYPP (Reynolds et al., 1997). Although K levels can be reduced by soaking (Table 2), neither alfalfa nor orchardgrass hay is a good option for horses diagnosed with HYPP due to the naturally high levels of K. Complete feeds specifically designed for horses diagnosed with HYPP offer an alternative feed option.
Table 2. Concentration of potassium in bud (AB) and flowering (AF) alfalfa hay and vegetative (OV) and flowering (OF) orchardgrass hay, before and after soaking in cold (C) or warm (W) water.
a-gvalues within a row not sharing a common superscript letter are significantly different (a statistical method used to separate results).
Dry Matter Loss
Soaking caused dry matter losses that increased with soaking duration. Losses in nutrients after soaking can be accounted for collectively by evaluating dry matter (DM) (Table 3). Dry matter losses were similar among the hay types after soaking for 15, 30 and 60 minutes. Dry matter losses for all hay types after soaking for 12 hours were greater than other soaking treatments. Failure to account for DM losses could lead to unwanted horse weight loss or stereotypic behaviors associated with low levels of forage in the diet, including wood chewing and cribbing (McGreevy et al, 1995). When soaking hay, additional hay should be soaked to account for the loss in DM.
Table 3. Dry matter losses from soaking bud (AB) and flowering (AF) alfalfa hay and vegetative (OV) and flowering (OF) orchardgrass hays in cold (C) or warm (W) water.
a-cvalues within a row not sharing a common superscript letter are significantly different (a statistical method used to separate results).
Owners should rely on forage analysis, both before and after soaking, as the primary method of determining the appropriate hay for horses, especially when feeding horses diagnosed with laminitis, PSSM, HYPP or COPD. For those horses, analysis of the NSC, P and mold content (for horses with COPD) of the forage is key. Hay soaking for short durations (15 to 60 minutes in duration) is an acceptable management method, but should only be used if preferred hay is not available. Soaking hay for longer durations (i.e., 12 hours) resulted in very low NSC content, high Ca:P ratios, a shortage of P in the diet, and high DM losses.
Soaked hay should be fed immediately to reduce the chance of mold. Care should be used when disposing of water after hay soaking. Water should be disposed of in random grassy areas and should not be accessible to horses.
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REVIEWERS: Jennifer Earing, PhD, University of Minnesota; Roy Johnson, Cargill; Jim Paulson, Univ. of Minn. Extension; and Sarah Ralston, VMD, PhD, Rutgers.
This article was co-authored by: K. Martinson, PhD; M. Hathaway; H. Jung, PhD; C. Sheaffer, PhD; University of Minnesota.