DYNAMICS OF PREFERENCE BY SHEEP OFFERED FOODS VARYING IN FLAVORS, NUTRIENTS, AND A TOXIN

We conducted two experiments to determine how toxicosis affected prefe rence of sheep for foods varying in flavors, nutrients, and a toxin. T he first experiment determined how toxicosis affected the preference o f lambs (fed a basal ration of alfalfa pellets) for foods that varied in energy and a toxin. Thirty lambs (10/treatment) were given LiCl by gavage (0, 50, or 100 mg/kg body wt/day), and 1 hr later were offered for 15 min/day foods containing different amounts (low, medium, high) of energy (barley) and a toxin (LiCl) added to alfalfa. The proportion s of barley and LiCl changed every three to six days during the 30-day study. The results showed: (1) lambs' food preferences were high > me dium > low for barley in the absence of LiCl; (2) lambs quickly regula ted intake of foods in response to changes in barley and LiCl concentr ations, even with short exposures (15 min/day); (3) lambs maintained i ntake of LiCl at about 57 mg/kg body wt by adjusting intake of food co ntaining LiCl in accord with the amount of LiCl they received by gavag e; and (4) as barley levels increased, intake of foods containing LiCl increased. The second experiment determined the relative influence of flavors, nutrients, and toxins on food preferences of lambs. We did t his by treatments in which different flavors (onion and oregano at 1%) were paired with different levels of energy (depending on the additio n of wheat to rabbit pellets) or a toxin (LiCl). At six-day intervals, we varied the types of food offered, either changing the nutrient or toxin content and the flavors. The resulting analyses of preference sh owed lambs markedly preferred foods high in nutrients and low in toxin s, regardless of flavor, when changes in food flavor were not correlat ed with changes in nutrient and toxin concentrations. Thus, in both ex periments lambs quickly regulated intake of foods varying in nutrients and a toxin according to the lambs' toxicological and nutritional sta te. Even with brief eating bouts lambs discriminated accurately and ex hibited little permanent preference or aversion in postconditioning pr eference tests. The lambs remained in an unbiased testing mode, sampli ng anew the food. This is adaptive because the toxin and nutrient cont ents of plants vary with season and location. Most taste aversion stud ies emphasize the permanence of aversions and miss the dynamic samplin g power of animals.