Intake Patterns of Sheep Offered Nutritious Alternatives Associated with Plant Secondary Compounds

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In grazing systems, ruminants can choose among plants with different nutritive value and different kinds and levels of plant secondary compounds (PSCs). In turn, their foraging decisions influence plant diversity. We investigated patterns of food intake by sheep fed two familiar nutritious diets (alfalfa and alfalfa-barley mixture) and three high-quality diets, each containing different PSCs (oxalates, tannins, and terpenes). The experiment consisted of two consecutive 8 day periods: conditioning and testing. During conditioning, the three PSC-containing diets were offered ad libitum while the two familiar nutritious foods were restricted to 300 g/d; during testing all five diets were offered ad libitum. In both periods, sheep were fed from 08:00 to 16:00 during which all diets were simultaneously offered to sheep and their intakes were recorded. During conditioning, consumption of all three PSCs increased (P≤0.001). Intake of the alfalfa-barley diet was the highest (984 g/d) during testing when sheep consumed more of the diet that contained tannin (471 g/d) than oxalate (181 g/d) or terpene (180 g/d). Intake of all diets across days was higher during the first hour than during the remaining hours (P≤0.001). These data suggest: (i) there may be several equally successful ways for animals to select their diets, particularly when more than two complementary diets are available; (ii) food intake increases when animals eat diets containing complementary PSCs; (iii) animals learned the benefits of such complementarities; and (iv) they continued to consume PSC-containing diets even when they had ad libitum access to other nutritious diets. This implies that grazing management can influence the foraging behaviour of animals by influencing the availability of alternative diets.

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