Soaking hay in water to reduce the sugar content of hay is very common and, for many people with horses diagnosed with laminitis, insulin resistance, polysaccharide storage myopathy (PSSM) or obesity, it’s become a routine part of their daily horse-keeping duties.

But, have you considered what the effects of soaking are on the hay’s nutrient profile and hygiene quality?

Fortunately for us, some researchers from the United States and United Kingdom have done just that.
Research conducted by Martinson and colleagues (2012) examined “The effect of soaking on carbohydrate removal and dry matter loss in Orchardgrass and Alfalfa hays” and “The effect of soaking on protein and mineral loss in Orchardgrass and Alfalfa hay”.

The researchers used four different types of hay of varying maturity, including a second cutting early bud alfalfa (alfalfa bud), a first cutting flowering alfalfa (alfalfa flower), a second cutting vegetative Orchardgrass (vegetative Orchardgrass) and a first cutting flowering Orchardgrass (mature Orchardgrass).
Sections of hay were randomly assigned to each treatment, which included soaking for 15 minutes, 30 minutes, 60 minutes or 12 hours in 25 litres of cold (22⁰C) tap water or for the same durations (but not 12 hours) in warm (39⁰C) tap water. Hay sections were then drained for 30 minutes and, for the purposes of the nutrient analysis, were dried at 60⁰C for 72 hours in an oven.

Carbohydrates

Reducing the carbohydrate content of the diet, specifically sugars and starch (also referred to as non-structural carbohydrates or NSC), is particularly important for horses diagnosed with laminitis, insulin resistance, PSSM or obesity.

When feeding such horses, it is recommended the dietary intake of non-structural carbohydrates (NSC) be less than 10% for PSSM-affected horses and less than 12% for obese, laminitic or insulin resistant horses. Previous studies have shown that such (lower) levels of NSC elicit a low or negligible glycemic response (insulin and glucose rise following sugar ingestion), whereas hay with higher NSC levels does elicit a glycemic response.

Current recommendations for soaking hay to reduce the NSC content are 30 minutes in warm water or 60 minutes in cold water.

This study confirmed that soaking hay in warm or cold water for 15 minutes, 30 minutes, 60 minutes, or 12 hours significantly reduces the NSC content of the hay compared to unsoaked hay.

How effective is soaking hay at reducing NSCs?

Percent loss of NSCs from Orchardgrass hay ranged from ~25% (15 minutes, cold water) to ~80% (12 hours, cold water), and from alfalfa hay ranged from ~17% (15 minutes, warm water) to ~70% (12 hours, cold water).  Between 40 and 50% of NSCs were lost after 60 minutes soaking in cold or warm water for all types of hay, with the exception of flowering alfalfa, which lost approximately 30% when soaked in cold water.

The Equi-Analytical feed profile database reports the NSC content of alfalfa hay to have a normal range of 8.7-13.2% NSC and grass hay to have a range of 8.0-17.6% NSC. Particularly for grass hays, the upper ranges are well above the recommended level of 10-12% NSC content for affected horses.

This study, therefore, confirmed the current soaking recommendations are sufficient to reduce the non-structural carbohydrate content of alfalfa and Orchardgrass hays to ‘safe levels’ for horses affected by NSC content. However, the great variability in NSC content emphasises the importance of having hay tested by a laboratory prior to feeding or being prepared to routinely soak hay prior to feeding.

What about the minerals?

Martinson et al conducted a second study to determine the effect of soaking on the mineral content. They found that while calcium was largely unaffected, other minerals, such as phosphorus, magnesium and potassium, were significantly reduced. This is an important finding because we know that mineral ratios are important when developing a balanced diet.

Calcium and phosphorus ratio

This is particularly so with calcium and phosphorus. The recommended Ca:P (calcium to phosphorous ratio) for mature horses is between 1:1 and 3:1. In this study, while calcium content was largely unaffected irrespective of water temperature or soaking duration, the phosphorus levels did decrease.

Soaking alfalfa hay for greater than 30 minutes resulted in a Ca:P of greater than 6:1 and as high as 10:1 when soaked for 12 hours. This change in Ca:P would have implications for accurately balancing diets and additional phosphorous may be needed to appropriately balance the calcium to phosphorous ratio.

Magnesium

The magnesium content of all hay types was reduced by soaking, with greater loss occurring with longer soaking times. Temperature had a greater affect on the magnesium loss for alfalfa bud and flowering Orchardgrass hays.

Potassium

This study also showed soaking hay in cold or warm water leads to a reduction in the total amount of potassium in alfalfa and Orchardgrass hays. For both types of hay, percent potassium loss ranged from 29-54% when soaked in cold water for 30 minutes, 31-61% when soaked in warm water for 30 minutes, 40-65% loss when soaked in cold water for 60 minutes and 72-80% loss when soaked in cold water for 12 hours.

Reducing the potassium content of hay would be of benefit to horses diagnosed with hyperkalemic periodic paralysis (HYPP) requiring a low potassium diet.

What about other nutrients?

Crude protein

Soaking the hay in water had variable effects on the crude protein content of the hay. There were no changes in crude protein content, compared to the control samples when alfalfa bud and flowering Orchardgrass hays were soaked. When flowering alfalfa was soaked, the crude protein content decreased slightly. In contrast, the crude protein content of the vegetative Orchardgrass increased with soaking. This was believed to be related to dry matter loss, increasing the relative concentration of crude protein.

Dry matter

Dry matter refers to the material remaining once all water has been removed from the feed during the preparation for analysis. Nutritionists will often refer to quantities of feed being fed on a ‘dry matter basis’ and this definition enables all feed types to be compared without the confusion created by the variations in water content. (The water content is relevant for other aspects as it will affect the actual quantity being fed.)
Some of the dry matter is lost during soaking (dissolves in the water and is lost) and this study found that losses of hay when soaked for 15 minutes, 30 minutes and 60 minutes in cold or warm water ranged from 11-16% for alfalfa bud, 9-12% for flowering alfalfa, 5-11% for vegetative Orchardgrass and 4-9% for flowering Orchardgrass.

The greatest dry matter losses were seen following 12 hours soaking where alfalfa bud lost 28% dry matter, flowering alfalfa lost 23% dry matter, vegetative Orchardgrass lost 17% dry matter and flowering Orchardgrass lost 20% of its dry matter.

Why is this dry matter reduction important?

Such alterations in dry matter mean the horse owner will need to compensate for this loss by feeding a larger quantity of soaked hay. For example, a 500kg horse receiving 2% of its bodyweight in hay would need 10kg hay per day. If this hay was soaked for up to 60 minutes resulting in 16% decrease in dry matter, the total quantity of hay would need to be increased by 1.6kg to 11.6kg prior to soaking. Likewise, if the hay was soaked for 12 hours, up to 2.8kg extra would be needed.

This is especially important for horses on hay-based diets (no pasture). Not accounting for the loss in dry matter over the long-term may lead to unwanted weight loss, digestive tract disorders, and potentially to the development of behaviours associated with low levels of forage in the diet, such as bed eating, coprophagy (eating manure), wood chewing and crib-biting.

What about hygiene and microbial contamination?

Unfortunately, there is a down-side to soaking hay. Researchers have previously reported that soaking hay for prolonged periods increases the bacterial contamination load and a recent study confirmed this.
Moore-Colyer et al (2014) took samples of Timothy mix meadow hay, Italian Rye Grass seed hay, pure Timothy seed hay, medium-cut Meadow hay and late-cut Meadow hay, and subjected the samples to soaking and/or steaming treatments.

Their soaking treatment involved immersing the hay in 30 litres of clean tap water (16°C) for nine hours, followed by 10 minutes hanging in the air to drain. The researchers reported the average bacterial contamination for the five hays types was increased five-fold following the nine hour soak.

Previous research by Moore-Colyer reported a 1.5-fold increase in bacterial contamination following a 10 minute soak in water. This rise in bacterial contamination is due to resident bacteria on the hay being washed into the soak water, where it is able to survive and rapidly multiply.

The researchers explained this is a great concern because an increase in bacterial contamination could increase levels of bacteria being ingested to above the recommended safe limit of 20 µg/g. Furthermore, they explained the “Ingestion of feed-associated bacteria will also mean the ingestion of significant levels of lipopolysaccharides, (the lipoglycans found in the outer membrane of Gram-negative bacteria), which can elicit undesirable strong immune responses in animals”.

In contrast, soaking the hay for nine hours in 30 litres of clean tap water (16°C), followed by air draining for 10 minutes, and then steamed for 40 minutes led to a reduction in the bacterial contamination by 98-99%. The researchers emphasised the steam needs to be maintained at a temperature above 90⁰C for a minimum of 10 minutes and completely penetrate all the hay to be effective at killing all the mould and most of the bacteria. Furthermore, they cautioned insufficient steam treatment could lead to increases in pathogenic bacteria, especially Thermoactinomyces spp, which thrive at temperatures of between 18-40°C.

In summary

Soaking hay using the currently recommended guidelines of 30 minutes warm water or 60 minutes cold water is sufficient to reduce NSC content to levels safe for horses with laminitis, insulin resistance, polysaccharide storage myopathy (PSSM) or obesity.

However, soaking hay for prolonged periods of time compromises the hygienic quality of the hay by increasing bacterial contamination, leads to substantial dry matter loss and increases the calcium to phosphorous ratio.

Ideally, hay should be analysed, so the non-structural carbohydrate content can be taken into consideration prior to soaking. If you have any concerns or questions regarding soaking hay, you should consult a qualified equine nutritionist.

NSC, ESC, WSC, Sugars, Starch… Are you confused?

Nutritionists and feed companies talk about NSC (non-structural carbohydrates) but, in practice, laboratory hay test results may provide the percentage of water soluble carbohydrates (WSC), ethanol soluble carbohydrates (ESC) and starch.

NSCs include a combination of water soluble carbohydrates (WSC), ethanol soluble carbohydrates (ESC) and starch.

WSCs include a combination of ESCs (simple sugars) plus complex sugars (polysaccharides including fructans).

Some of these polysaccharides, such as fructans, do not affect the glucose and insulin response in the horse because they are not digested in the small intestine.

Here’s how to keep it simple: 

When feeding insulin resistant equines the best practice is to combine (add) the ESC and starch content and ensure that the total is below 10%.

If the feed product is labelled and the label states that the NSC content is below 10%, then you can be safe in the knowledge that total ESC and starch content will also be under 10%.

When sending your hay for testing in a laboratory, check that they will provide the starch values so you can make the calculation. Unfortunately, not all hay testing services offer starch values as a routine.

References

  • Martinson K, Jung H, Hathaway M, Sheaffer C. (2012) The Effect of Soaking on Carbohydrate Removal and Dry Matter Loss in Orchardgrass and Alfalfa Hays. Journal of Equine Veterinary Science 32 (2012) 332-338 http://www.sciencedirect.com/…/pii/S0737080611006678
  • Martinson K, Hathaway M, Jung H, Sheaffer C. (2012) The Effect of Soaking on Protein and Mineral Loss in Orchardgrass and Alfalfa Hay. Journal of Equine Veterinary Science 32 (2012) 776-782. http://www.sciencedirect.com/…/pii/S0737080612001049
  • Moore-Colyer MJS, Lumbis K, Longland A, Harris P (2014) The Effect of Five Different Wetting Treatments on the Nutrient Content and Microbial Concentration in Hay for Horses. PLoS ONE 9(11): e114079. doi:10.1371/journal.pone.0114079