Dietary monoterpene concentrations influence feeding patterns of lambs

Monoterpenes in plants can adversely affect herbivores. To minimize toxicity, herbivores may regulate their patterns of feeding to limit intake of monoterpenes. We determined if diets with four concentrations of monoterpenes (0%, 1.55%, 3.10%, 4.65% DM) influenced feeding patterns of lambs by measuring food intake and percentage time lambs spent feeding on the four diets. During the first trial, lambs were offered terpene diets ad libitum from 0900 to 1200 h for 6 d; they were then fed a maintenance ration of alfalfa pellets in the afternoon of each day. During the second trial, lambs were offered terpene diets ad libitum from 0900 to 1500 h for 4 d, but they did not receive the maintenance diet of alfalfa pellets. In the first trial, food intake was lower when monoterpene concentrations were high and intake of monoterpenes reached a threshold at 27-28 g/d monoterpenes. All lambs consumed more food in the first hour than during the latter hours of feeding (P < 0.001). While the percentage of time spent feeding was the same for the control-, low-, medium-, and high-terpene groups, lambs fed the high-terpene diet spent more time feeding in hour 3 than lambs fed the control diet (P < 0.05). In the second trial, when alfalfa pellets were not offered as a basal diet, lambs offered the control- and low-terpene diets consumed a relatively large proportion of food during the first hour. Intake remained low for the medium- and high-terpene diets over the 6-h period (P < 0.001). We conclude monoterpenes limited food intake and caused lambs to regulate feeding patterns in a way likely to reduce the possibility of ingesting toxic quantities of monoterpenes.