Stack Builder

What a stack is — and why the total matters

A stack is the combination of several compounds fed to a horse at the same time: magnesium, vitamin E, biotin and a herbal component, for instance, spread across two or three complementary feeds. Each individual product is dosed and declared on its own. What no label shows is the total across all products together — and that is exactly where most errors arise.

The Stack Builder starts at this point. For every compound selected it calculates a weight-related daily amount, checks the combination against the stored synergies and interactions, and shows the FEI status for competition horses. The result is a calculated guide value, not a feeding instruction.

Dose per kilogram of body weight

Many directions on complementary feeds refer to a standard horse of 500 or 600 kilograms. A 200-kilogram Shetland pony and an 800-kilogram draught horse would then get the same amount — arithmetically four times as much per kilogram for the pony. That is why the builder uses the entered weight wherever the data provide a figure per kilogram of body weight. If no weight is stored, it assumes 500 kilograms and says so.

Not every compound can be scaled this way. For some herbs and vitamins only amounts per animal are available, taken from studies with a particular reference weight; they appear as a reference range and are not scaled up. Trace elements such as selenium and amino acids such as lysine, by contrast, are given per kilogram of dry matter of the whole ration, because that is how NRC 2007 and the GfE phrase their recommendations.

For energy requirements the recommendations work with metabolic body weight, that is, body weight to the power of 0.75 — the feed requirement calculator uses exactly that. For most additives no comparably well-founded scaling exists. The builder therefore keeps to the linear figure of the source rather than suggesting a precision the data cannot support.

Overlaps and maximum contents

The most common error is not the wrong compound but the duplicated one. Zinc is in the mineral feed, in the hoof supplement and often in the muesli as well; selenium in the mineral feed and in the vitamin E supplement. Each product complies with the rules on its own, but the total does not necessarily.

In the EU, trace elements are feed additives under Regulation (EC) No 1831/2003. For every authorised trace element a maximum content per kilogram of complete feed is set, based on 12 percent moisture. For selenium this value is 0.5 milligrams in total — with this element the gap between requirement and oversupply is particularly small. Maximum contents also apply to copper and zinc.

Ratios come on top of that. A high zinc share is associated in the literature with reduced absorption of copper, which is why feeding recommendations consider both elements together. The builder flags such pairs. It does not know the actual contents of the basic ration and the mineral feed — those belong on the table before any supplementation.

Synergies and interactions

As synergies the builder shows combinations that are discussed together in studies and specialist literature: vitamin E and selenium as an antioxidant pair, vitamin B6 as a cofactor in the metabolism of tryptophan. This does not mean the combination achieves more than the individual compounds. It means that both compounds belong together in nutritional terms and should be considered together.

Interactions are the opposite direction: compounds that hinder each other's absorption or whose combination calls for additional attention. There are also notes derived from the stored horse data — pregnancy, senior age, foals or recorded pre-existing conditions. Such a note is a classification of the compound, not a statement about the individual animal.

FEI status and withdrawal in competition

In its Equine Prohibited Substances List the FEI distinguishes two groups: Banned Substances, which may not be used in equestrian sport at all, and Controlled Medication, whose use outside competition may be permitted but which must not be detectable in competition, or, for threshold substances such as salicylic acid, not above that threshold. Plant-based compounds can be affected too — capsaicin from chilli, for example, is listed as a Banned Substance.

Choosing FEI international or racing as competition status switches on Clean Sport mode. Prohibited compounds are then locked and no longer recommended; compounds in the Controlled Medication group carry a withdrawal note. For all other competition levels the FEI status stays visible as information.

The detection times published by the FEI are not guaranteed withdrawal times. They describe detection periods under study conditions; dose, form of administration and the individual horse can shift them. The list is revised every year on 1 January, and national rules may differ. Before every competition the current version counts, not the state of a calculator.

Feed, not medicine — and what the builder does not know

Everything in the builder is intended as feed: complementary feed within the meaning of Regulation (EC) No 767/2009, in some cases dietetic feed. Under Article 13 of that regulation, feed may not be advertised with disease-related promises. Veterinary medicinal products, by contrast, fall under Regulation (EU) 2019/6 and, in Germany and Austria, under the respective Veterinary Medicinal Products Act (TAMG). Prescription-only veterinary medicines do not belong in a stack; whether and how they fit with feed additives is for the vet to decide.

The builder knows neither the basic ration nor hay quality, blood values or current medication. It is therefore no substitute for a ration calculation: forage is assessed first and the mineral feed matched to it, and only then does supplementation come into question. With pre-existing conditions, pregnancy or medication, the stack belongs with a vet or a feeding advisor before use.

• NRC 2007 — Nutrient Requirements of Horses, 6th revised edition, National Research Council
• GfE 2014 — Recommendations for energy and nutrient supply of horses, Gesellschaft für Ernährungsphysiologie, DLG-Verlag
• FEI 2026 — Fédération Equestre Internationale — Equine Prohibited Substances List 2026 (in force from 1 January 2026) and FEI List of Detection Times
• VO (EG) 767/2009 — Regulation (EC) No 767/2009 on the placing on the market and use of feed, in particular Art. 3 (complementary feed) and Art. 13 (labelling and advertising)
• DVO (EU) 2019/804 — Commission Implementing Regulation authorising an organic form of selenium as a feed additive — maximum 0.50 mg total selenium per kg complete feed (12 % moisture)