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That sainfoin is repeatedly criticised as a horse feed is nothing new. What is new, is that it is said to have a negative impact on the health of the thyroid gland due to increased iodine requirements. The often-cited thiocyanates are indeed able to contribute to increased iodine excretion. However, thiocyanates belong to the so-called ubiquitous substances, which means that they are found everywhere. All animal cells resp. intercellular fluids contain thiocyanates and one of the largest producers are liver cells (1). During evolution, the organism has found ways of dealing with certain quantities, otherwise mammals would have already died out.

As early as the 1990s, studies showed that thiocyanates do not inhibit the uptake of iodine into the thyroid gland in the physiological range; at most, there was evidence that it is slightly stimulated (2,3). There is only an increase in iodine excretion, and this only becomes a problem if the animals are not fed a mineral balancer (4,5,7). Commercial mineral feed balancers are in general balanced with trace elements, including iodine, usually as calcium iodate. This ensures the supply and even an increased content of thiocyanates does not automatically lead to iodine deficiency.

In addition, thiocyanates have so far only been detected in the seeds of alfalfa, for example, which is very closely related to sainfoin. As soon as the seed germinates, these thiocyanates are broken down so that no significant levels can be detected in the adult plant. The digestibility resp. thiocyanate content of alfalfa seeds plays a role in human nutrition, where seeds of various plants are increasingly being used as novel foods, especially in vegetarian or vegan diets (6).

In horses, however, the internode or stem of the whole plant is fed so that there are no longer any problems with thiocyanates. It is sometimes pointed out that whole plants, such as rapeseed or field mustard, also contain glucosinolates and therefore have a negative effect on the thyroid gland. Glucosinolates belong to the cyanogenic glycosides, which can have a considerable effect on thyroid function and are broken down into thiocyanates in the body (6).

If you take a closer look at botany, you will realise that sainfoin, just like alfalfa, belongs to the Leguminosae plant family, while field mustard and rapeseed belong to the Brassicaceae plant family. We are talking about different plant families, which therefore have very different properties. The Leguminosae (“legume, pea, or bean family “) are able to colonise so-called nodule bacteria on their roots.

These make nitrogen available to the plant, which means that all Leguminosae have a very high protein content. This is utilised in nutrition as well as feeding: soya, bean or pea products are used as a protein-rich meat substitute on the dinner plate. Lucerne and sainfoin have been successfully used in animal feed for centuries. The Brassicaceae (“Cruciferae vegetables”), on the other hand, are the plants of the cabbage family. This includes rapeseed as well as broccoli. As nobody would probably think of feeding their horse raw broccoli, there is no need to worry about the glucosinolates contained in Brassicaceae in horse feed.

Read more: is that correct? .


1) Carlson et al.: Volume dilution of sodium thiocyanate as measure of extracellular fluid volume in the horse, Am. J. Vet. Res. 1979

2) A. Kramer et al: Experimental and epidemiological studies on the interaction of thiocyanate and thyroid function. In: Z ges Hyg. 36, 1990, pp. 383-387.

3) Virion et al: Opposite Effects of Thiocyanate on Tyrosine Iodination an Thyroid Hormone Synthesis, European Journal of Biochemistry, 1980

4) Schoene et al: Evaluation of linseed feedstuffs (ground linseed, solvent extracted linseed meal) with growing pigs – feed value, thiocyanate and thyroid hormone status, AGRIS 1997

5) Dunn and Dunn: Update on Intrathyroidal Iodine Metabolism, Thyroid, 2004

6) Malinow et al: Alfalfa seeds: Effects on cholesterol metabolism, Experiencia, 1980

7) Lopez-Rodriguez et al: Effects of the Glucosinolate Sinigrin in Combination With a Noniodine Supplemented Diet on Serum Iodine and Thyroid Hormone Concentrations in Nonpregnant Mares, J. Equine Vet. Science, 2020