Linseeds and soy beans are oil-rich plant seeds that are also good sources of protein for horses. Both are used in feed manufacture as well as being available as straight supplements.
For horses who aren’t in work, growing, or breeding, good quality forages including pasture and conserved hay and haylage provide enough good quality protein. For those with higher requirements, however, levels from grass forage will not suffice.
Both linseed and soy beans can be fed as a meal after the oil is extracted, or whole, still containing the oil. The difference nutritionally is protein as well as oil content. The meals after oil extraction are (obviously) lower in oil but also higher in protein, and are important ingredients in animal feeds. The whole (processed) seeds are becoming more popular as a high calorie feed supplement that supplies good levels of good quality protein.
Linseeds are about 40% oil, 25% protein and 3.9% lysine. They contain lignan, a phytoestrogen compound with antioxidant properties, and soluble fibre, which is described as mucilage. Linseed oil is the richest vegetable source of healthful omega-3 fatty acids, and the whole (processed) seeds contain about 19% alpha-linolenic acid. After oil extraction, the meal contains 3.5% oil, 36% protein and 3.9% lysine.
Soy beans are about 21% oil, 40% protein and 6.2% lysine. They contain some sugars, insoluble fibre, lecithin, phytosterols and phytoestrogens. Soy beans are the richest source of lysine of all vegetable feeds for horses. After oil extraction, the meal contains 2.2% oil, 51% protein and 6.1% lysine. The meal obtained is actually more valuable than the oil that is extracted. Soya tends to be the main source of protein in good quality compound feeds for working, breeding and growing horses.
Linseed and soy beans both contain antinutritional factors, which mean they must be cooked (heat-processed) to inactivate these toxins, before being fed to horses. Micronising and steam flaking are two commonly used processes that makes them safe without taking away any goodness.
Both seeds and meals supply no starch and have a relatively low sugar content – at around 4% for linseed and 10% for soy. Both seeds and meals have an inverse calcium to phosphorus ratio for horses, so if added in quantities over 500 g daily, or to low calcium diets, extra calcium may need to be fed.
Whole micronized linseeds, linseed meal, whole flaked soya and soy bean meal are useful supplementary feeds for horses that can be fed safely in limited quantities without unbalancing the diet, and provide excellent sources of protein without adding unwanted starch or sugar.