Phytate (phytic acid) is the primary storage form of phosphorus in grains, seeds, and legumes. While it contributes phosphorus to your horse's diet, phytate also binds zinc, copper, iron, and calcium in the gut, reducing their absorption. For horses on grain-heavy diets, this mineral-binding effect can be nutritionally significant — a diet that looks adequate in zinc and copper on paper may actually deliver less than expected because phytate is sequestering those minerals before they can be absorbed. Horses are somewhat better at handling phytate than monogastric animals like pigs or dogs, because hindgut bacteria produce some phytase enzyme that breaks down phytate and releases bound minerals. However, this microbial rescue is partial, not complete.
There is no target phytate level to aim for — the goal is simply to be aware that grain-heavy diets may require higher mineral supplementation to compensate for phytate binding. If your horse receives more than 3 to 4 kilograms of grain or concentrate per day, ensure zinc, copper, and iron supplementation accounts for reduced bioavailability. Feeding forage as the majority of the diet naturally limits phytate exposure.
Phytate is not a nutrient, so there is no deficiency. The concern is that high phytate intake from grain-heavy diets can cause secondary mineral deficiencies — particularly zinc, copper, and iron — leading to poor coat quality, weak hooves, impaired immune function, and slow wound healing.
Horses on diets very high in unprocessed grains or bran (wheat bran was historically a common feed) can develop mineral imbalances. Wheat bran is particularly problematic because it is very high in phytate and has an inverted calcium-to-phosphorus ratio, which is why the old practice of feeding bran mashes has fallen out of favor.
