Soaking & Steaming Hay
Soaking hay and steaming it can benefit horses with respiratory issues, laminitis and those that are sensitive to sugar or require low potassium content.
Hay is a staple of the equine diet, but some horses have trouble eating it, according to this Horse Sport article. If it is dusty or mouldy it may trigger respiratory problems such as chronic obstructive pulmonary disease (heaves). Hay that is high in non-structural carbohydrates (sugars and starches) is unsuitable for horses that tend to founder, are laminitic, or challenged by metabolic syndrome. As potassium tends to be high in hay regardless of type, it may not be good for horses with hyperkalemic periodic paralysis (HYPP) who require a low-potassium diet. Dry, stemmy hay can be difficult for older horses with poor teeth to chew.
Moistening hay via soaking or steaming can make it more manageable for these types of horses, reducing the sugar and potassium content, killing mould, and making it more palatable for senior animals.
To read more, go to: https://horsesport.com/magazine_articles/benefits-soaking-steaming-hay-horses