horse standing in drylot during winter

Q: What nutrient deficiencies are common in horses, especially in the winter, and what are some signs to watch for?

A:  For horses that are stabled year-round, there will not be much difference in their nutrient intake from season to season. However, for horses that have access to good-quality pasture in the spring, summer, and fall, shifting to a hay-based diet in winter could result in some new challenges, specifically involving adequate protein, vitamin E, and omega-3 fatty acids. These issues exist for the horses stabled and on hay year-round, but they are not winter-specific for these horses the way they are for those that have pasture access in other seasons.

Pasture grass can be an abundant source of vitamin E and omega fatty acids if it is good-quality and horses have adequate access, meaning you don’t need to supplement their forage with additional hay because the pasture is fully meeting those needs. The problem is neither vitamin E nor omega fatty acids are particularly heat stable. This means when the grass is cut and laid out in the sun to cure, much of it is lost. So, horses on hay-based diets are consuming far lower amounts of these essential nutrients and, therefore, we recommend providing additional sources.

Horses that receive a good-quality ration balancer or other commercial feed fed at the correct manufacturer-recommended intake, should be receiving adequate vitamin E to meet their National Research Council (NRC) recommended daily requirement. However, owners often feed these incorrectly, offering far less than the manufacturer recommends for their horses’ weight or work level. Further, feeds commonly use synthetic sources of vitamin E, which is not as bioavailable as natural vitamin E and less likely to meet the horse’s needs.

The incorrect feed intake and lower bioavailability can leave horses being deficient in vitamin E, even when on paper it appears their NRC needs are being met. Additionally, the utilization of vitamin E varies greatly from horse to horse. The same diet could be fed to three horses with the exact same vitamin E requirements, and one might have serum levels that are deficient, another normal, and the third above normal. Therefore, the only way to know for sure is to test your horse’s serum vitamin E levels, which is a good thing to do in winter to make sure the hay-based diet is doing its job.

Horses that are on hay year-round can be tested when convenient, but in performance horses I recommend testing as their work gears up for competition to make sure they’re being set up for success going into the season.

Providing a source of omega-3 fatty acids is most easily done by feeding ground stabilized flax or an oil such as flax oil, camelina oil, or fish oil. Horses without access to adequate omega-3 fatty acids might have a dull coat and poor skin quality. Low vitamin E can also be reflected in coat quality but is linked to muscle soreness, poor performance recovery, and lack of topline development.

Quality protein is also important for topline development and maintenance, and while most hays provide adequate crude protein, it is not always the best quality. This is especially true in more mature stemmy hays, which have a higher amount of indigestible fiber that might impact protein availability. A lab test might show adequate amounts of crude protein, but in the digestive tract it might not be available to the horse.

This is again where a good ration balancer can save the day, as these are typically quite high in protein and guarantee good levels of the typically limiting amino acids lysine, methionine, and threonine. Good performance and complete feeds can also provide these, as long as they are fed in the quantities recommended.