Organic Silicon in Plants as a Limiting Factor of Forage Digestibility in the Nutrition of Herbivorous Mammals

The effect of organic forms of silicon contained in plant tissues on the digestibility of feed for herbivorous mammals has been studied. In the process of digestion, an extremely small part of the consumed silicon is assimilated, which makes it possible to use organic silicon naturally contained in plants as an indicator of the digestibility of plant foods. The consumed silicon reduces the digestibility of the feed, puts a limit on the fermentation of the consumed vegetable substrate and its structural components (fiber, lignin). With an increase in the part of silicon in the consumed vegetation per unit, the digestibility decreases linearly by 3–4 units. The fermentation limit is set when the silicon content in the feed is within 3–4% of the dry weight. Among the main groups of forage plants (grasses and forbs), the amount of silicon is significantly higher in grasses (1.70 and 0.91%, respectively). For this reason, the digestibility of grasses in all compared animals (camels, Przewalski’s horses, bison, saiga) is 1.2–1.4 times lower than the digestibility of forbs. With an increase in the proportion of grasses in feed per unit, the digestibility of feed in animals with different types of digestion (ruminant, monogastric) decreases linearly by an average of 0.16 units. The different digestibility of grasses and forbs causes the separation of herbivores by types of nutrition and food specialization. Consumers of various forbs (saigas) avoid the consumption of grasses and are not viable with their dominance in pasture vegetation. The specific features of the digestion of herbivores (Equidae, Bovidae) provide an increased volume of consumption, compensating for the reduced digestibility of grasses.