Question
I’ve recently purchased a horse for my daughter, which will be kept at a local boarding stable. I work in the dairy industry. Because high-quality nutrition fuels milk production in cows, I have a working knowledge of ruminant nutrition. When I was looking over the ingredients listed on empty horse feed bags at the stable, I noticed that horse feed doesn’t ever seem to contain non-protein nitrogen sources. The few bags I scanned seem to contain a single protein source, soybean meal. Why?
Answer
As you mentioned, non-protein nitrogen sources are frequently used in the diets of ruminants, such as dairy and beef cattle. These feed ingredients provide nitrogen to the microflora of the rumen to aid in the production of microbial protein, which can then be used to meet a significant portion of the ruminant’s protein requirement. Even though non-protein nitrogen sources, like urea, are generally more economical than plant- or animal-based protein sources, they are used sparingly in cattle feeds because palatability decreases as inclusion rate increases. Other feedstuffs used concomitantly to supply ruminants with protein include soybean meal, corn gluten, and dried distillers grains, among others.
Researchers have found that most horses, unlike cattle, do not benefit from urea consumption due to anatomical and physiological differences of their gastrointestinal tract. In digestibility studies, only certain horses obtained minimal benefit from urea, namely those fed diets containing marginal protein.
With this in mind, conscientious horse feed manufacturers typically choose to incorporate soybean meal into their formulations. Soybean meal is considered a high-quality protein because it contains an amino acid profile generally considered superior to most other seed meals, such as cottonseed meal, sunflower seed meal, and canola meal. Many seed meals are low in lysine when compared to soybean meal. Lysine is the first limiting acid in horses, meaning that without sufficient quantities of it, other amino acids cannot function as they should.
Concern about urea toxicity in horses has also been debated. While toxicity has been induced in experimental situations, few horses would consume the amount of urea necessary to bring about poisoning. Nevertheless, the potential for toxicity is possible, so a fortified feed made by a reputable manufacturer specifically for horses should always be fed. Feed intended for cattle should not be fed to horses. Not only may cattle feed contain urea or another non-protein nitrogen feedstuff, but it might also contain additives that are without question toxic to horses, such as ionophores.
