You can feed beautiful-looking hay, offer plenty of it, and still end up with a ration that is incomplete. That is the heart of the question horse owners keep asking: what nutrients are missing from hay? The answer is not that hay is poor feed. Far from it. Hay is the foundation of a horse’s diet. But even good hay is rarely a complete source of every nutrient a modern horse needs.
This matters because roughage-first feeding only works well when the roughage is understood for what it is: the base, not always the full ration. As Annette explains in The New Feeding, feeding becomes much clearer when you start with the horse’s natural need for forage and then correct the gaps thoughtfully, rather than piling on unnecessary concentrates.
What nutrients are missing from hay most often?
Hay usually provides fiber and energy first. Depending on the grass species, soil, harvest timing, and storage, it may also contribute some protein, minerals, and vitamins. The problem is that those levels are highly variable. Hay is not made to a fixed recipe.
The nutrients most often missing from hay, or present in too low an amount, are trace minerals, certain vitamins, and sometimes quality protein. In practical terms, horse owners most often need to pay attention to copper, zinc, selenium, iodine, and vitamin E. Calcium and phosphorus can also be unbalanced, not always truly missing, but present in a ratio that does not support the whole ration well. Sodium is another common gap, since hay naturally contains very little salt.
That does not mean every bale is deficient in every one of these nutrients. It means hay alone often leaves blind spots, especially when it is the main or only feed source.
Why hay can never be judged by appearance alone
A clean, green, sweet-smelling hay may look ideal, and from a hygiene and intake perspective that matters a great deal. But appearance tells you very little about micronutrient content. Two hay lots can look nearly identical and have very different mineral values.
Soil plays a major role. Grass grown on one field may be low in selenium or copper, while another field nearby may differ completely. Fertilization strategy, cutting stage, weather, and storage time all influence the final nutrient profile too. Once hay is cut and dried, some vitamins decline further during storage, especially vitamin E and carotene, which is the precursor to vitamin A.
This is where many feeding mistakes begin. Owners assume that because hay is natural, it must be nutritionally complete. Natural does not always mean balanced.
The nutrients hay does provide well
Before focusing only on shortages, it helps to recognize hay’s strengths. Good hay is the horse’s main source of structural fiber, which supports normal chewing time and natural digestive function. It can also provide a meaningful amount of calories and, in some cases, decent crude protein.
For easy keepers or horses in light work, hay may cover much of the energy requirement. For horses with higher demands, such as growing horses, breeding mares, and sport horses, the challenge is often not just total energy but the concentration of nutrients per kilogram of feed. Hay fills the gut well, but it does not always deliver enough micronutrients in proportion to the horse’s needs.
That distinction is important. A horse can eat enough hay to feel full and still not receive a well-balanced ration.
Trace minerals are often the biggest issue
If you ask what nutrients are missing from hay in the most practical day-to-day sense, trace minerals are usually the first place to look. Copper and zinc are especially common concerns in forage-based rations. These minerals are needed in small amounts, but they matter because they are involved in many normal body processes and tissue development.
Selenium is another nutrient that depends heavily on local soil conditions. In some regions, forage contains very little. In others, levels may be less predictable. That is exactly why supplementation should be targeted rather than guessed.
Iodine can also be low in forage-only diets. Since hay contributes little sodium as well, horses on hay without added salt are often left with an obvious gap in the ration.
These are not dramatic issues you can always spot at a glance. More often, they are quiet imbalances in the background of the feeding plan.
Vitamins in hay decline over time
Fresh pasture and hay are not nutritionally identical. Once grass is cut, dried, and stored, some vitamin content begins to fall. Vitamin E is one of the best-known examples. Horses on fresh grass usually consume far more natural vitamin E than horses on stored forage.
Carotene also decreases with storage, which matters because it is converted into vitamin A. Well-made hay still has value, but the longer and more intensively it is stored, the less you should assume it will cover vitamin needs on its own.
This is one reason winter rations often need closer attention than summer grazing diets. The forage may still be plentiful, but it is no longer nutritionally equivalent to fresh grass.
Is protein missing from hay?
Sometimes yes, sometimes no. Protein is one of the more misunderstood parts of a hay-based ration because people tend to think in terms of total percentage only. What matters more is whether the hay supplies enough usable protein for the horse’s life stage and workload.
Late-cut hay often contains less protein than earlier-cut forage. Mature grass hay may be perfectly acceptable for an easy-keeping adult horse at maintenance, yet too limited for a young horse, broodmare, or horse needing topline support. In those cases, the issue may not just be quantity but amino acid quality.
So while protein is not always one of the nutrients missing from hay, it can be insufficient in certain situations. This is where ration balancing becomes more precise. You are not asking whether hay is good or bad. You are asking whether this hay is suitable for this horse.
Calcium, phosphorus, and the balance question
Hay often contains a reasonable amount of calcium, especially if legumes are present, but phosphorus may be lower. Grass hay is not automatically wrong in this regard, yet the ratio between these minerals can drift away from what is ideal when no balancing feed is added.
For adult horses at maintenance, this may not create obvious short-term concerns. For growing horses, pregnant mares, and horses with greater nutritional demands, mineral balance deserves more attention. A ration can look simple and sensible while still being uneven underneath.
That is one of the key lessons in a modern roughage-first approach: balancing is not about feeding more products. It is about correcting what forage does not reliably provide.
When hay alone may be enough, and when it usually is not
There are horses that manage well on hay plus water and salt for a period of time, especially easy keepers in light work. But even then, "managing" is not the same as having a fully balanced ration.
The more demanding the situation, the less likely hay alone is to be enough. Young horses need carefully supplied building blocks. Breeding horses need consistency. Performance horses need nutrient density without excessive starch. Older horses may need support for intake, chewing efficiency, or body condition. In all of these cases, relying on hay alone becomes increasingly risky.
Hay analysis can help reduce guesswork. If you know the forage values, you can make much better decisions about what truly needs to be added and what does not.
How to fill the gaps without overcomplicating the ration
The best feeding plans are usually simpler than people expect. Start with enough hygienic, good-quality forage. Then ask what that forage is unlikely to cover. In many cases, the answer is a well-formulated vitamin and mineral balancer, along with salt and access to water. Some horses will also need additional protein or energy, but that depends on the individual.
This is where horse owners often go wrong by adding multiple products for separate concerns without checking whether the foundation is balanced first. A horse does not benefit from a complicated ration if the basic mineral supply is still off.
A targeted balancer makes sense because it adds concentrated nutrients without forcing you to feed large amounts of concentrate. That fits the roughage-first principle well. It also keeps the ration easier to understand, which is one of the most valuable parts of a good feeding strategy.
The real answer depends on the hay and the horse
So, what nutrients are missing from hay? Most often, the missing pieces are trace minerals, salt, and vitamins that decline during storage, with protein and major mineral balance depending on hay type and the horse’s needs. That is the honest answer. Not every hay is the same, and not every horse asks the same thing from its ration.
The goal is not to replace hay. It is to respect hay for what it does best and then support it where it falls short. When feeding is built that way, it becomes calmer, clearer, and much more logical - for both horse and owner.
A good ration does not start with the question, "What should I add?" It starts with, "What does my forage provide, and what does it still need?"