Feeding forage first—whether through grazing or hay—is considered a best practice when building a ration for most horses. Exceptions to this rule are horses with insulin resistance or metabolic conditions.

“The minerals I see most commonly lacking in forage-based diets are copper and zinc,” said Clair Thunes, PhD, owner of Clarity Equine Nutrition. “When the diet is hay-based, vitamin E can be deficient because it is not heat stable. So, while it is abundant in good-quality fresh pasture grass, it is very low in hay.”

The first step is to confirm which nutrients are missing in a forage-only diet. Ordering a forage analysis provides insight into the available protein, minerals and digestible energy. However, it is worth noting that while on paper these sources might provide adequate vitamin E, some horses will still be deficient. Therefore, it is advisable to have a veterinarian test the horse’s serum vitamin E level to determine if an additional vitamin E supplement is warranted, according to Thunes.

Offering access to a mineral salt block might be enough to make up for any deficiencies in other minerals.

“If the horse is maintaining their weight adequately on forage alone, a low-calorie ration balancer is an ideal way to provide the missing pieces,” Thunes said. “These typically have a low feeding rate of 1 to 2 pounds for most horses and are highly fortified.”

Horse owners know that too much selenium can be problematic, but selenium deficiencies are also possible in some parts of the country or with some forages. Horses need 1 to 3 mg of selenium per day. Selenium levels vary geographically, so it’s important to know what’s in your grass and hay—especially when it is shipped in from another region.

Working with a veterinarian and equine nutritionist is always recommended before making significant ration changes to ensure your horse gets the nutrients he needs to stay healthy.