Q. I’d like to soak my horse’s grass hay to reduce sugar and dust content. Do I need to be aware of anything specific when feeding soaked hay?
A. Soaking can be a good way to reduce dust and sugar in hay and is a tool often used by owners managing horses with equine metabolic syndrome or equine asthma. Researchers have performed a number of studies trying to quantify just how much water-soluble sugar soaking removes and what impact soaking has on dust.
Work conducted at the University of Minnesota has shown that soaking a variety of hays for as little as 15 minutes in cold or warm water can reduce nonstructural carbohydrate (NSC) content. Interestingly, in nearly all cases NSC loss was higher when using cold water, although the difference was typically not significant and other studies have shown warm water to be more effective. Across studies though, the longer the hay soaked, the greater its NSC loss.
Keep in mind that soaking hay might not make it safe for horses with metabolic issues. Horses with insulin dysregulation, for instance, should ideally consume a hay with less than 10% NSC. The amount of NSC removed with soaking varies based on hay type, soaking length, water temperature, etc. What we do know is that a hay will have lower NSC after soaking than before. If possible, send soaked hay to a lab for analysis to confirm it’s safe to feed a horse with equine metabolic syndrome or insulin dysregulation.
One study showed that soaking had no impact on the crude protein content but did reduce the level of some minerals in the hay. Soaking for 60 or more minutes reduced potassium levels, which might interest owners managing horses with hyperkalemic periodic paralysis (HYPP) that need low-potassium diets. Hay soaked for 12 hours lost enough phosphorus that it could result in a phosphorus-deficient ration if fed to meet the needs of a 500-kilogram (1,100-pound) horse in light work. Other studies have also shown significant reductions in potassium and phosphorus, as well as magnesium, sodium, and copper even in hay soaked for as little as 30 minutes.
This length of time also significantly reduces the number of respirable particles smaller than 5 micrometers. In a Royal Agricultural College study, researchers measured particles captured while shaking hay for nine minutes after soaking. The data were expressed as numbers of particles present per liter of air sampled and per kilogram of hay shaken. Unsoaked hay had 25,971 particles. Soaking hay for 10 minutes reduced particles to 1,862, and soaking for 30 minutes reduced particles to 1,163.
Based on these findings and others, veterinarians and nutritionists typically recommend soaking hay for no longer than 30 to 60 minutes, a length of time that effectively lowers dust and NSCs while minimizing nutrient loss.
There are other considerations beyond length of soak time. Soaked hay has less dry content due to the water it absorbs. Horses generally need to consume 1.5-2% of their body weight in dry matter per day. Therefore, to avoid weight loss, you might need to feed more soaked hay than you would dry.
Another important consideration is mold. Feed soaked hay immediately after soaking and don’t allow it to sit uneaten for long periods, because it can start to ferment, especially in hot weather. Soaking hay isn’t always feasible if you live in an area with drought or freezing winter weather. For this reason, finding hay that is nutritionally appropriate without soaking is ideal. For horses with equine asthma, hay steaming is another option that can be done in any climate and is very effective at removing dust, mold, and fungi from hay.