Food deprivation affects preference of sheep for foods varying in nutrients and a toxin.

We investigated how food deprivation affected preference of lambs for foods that varied in concentrations of nutrients and a toxin. Thirty lambs (10 lambs/treatment) were fed different amounts of alfalfa pellets (high in protein, marginal in energy for growth) as a basal ration (20, 40, or 60 g/kg body weight). Every morning, prior to ingesting the basal ration of alfalfa pellets, each lamb was offerend three foods for 15 min. The foods contained different amounts of energy and a toxin, depending on the addition of barley (energy) and LiCl (toxin) to alfalfa. The proportions of barley and LiCl changed every five days during the 25-day study. The results showed: (1) all lambs preferred food that was high > intermediate > low in energy (barley) in the absence of LiCl, but all lambs decreased consumption of foods high in energy as LiCl concentrations increased; (2) the greater the level of food deprivation, the lower the consumption of foods containing LiCl, even if the foods provided high levels of energy; (3) lambs moderately food deprived or fed ad libitum ingested more LiCl than lambs that were highly deprived; and (4) lambs quickly (15 min/day) regulated intake of foods in response to changes in barley and LiCl concentrations. Thus, our results suggest that the interaction between nutritional status and toxicosis plays an important role in food preference of lambs. Our findings also suggest that toxic plants may kill herbivores that lack nutritious alternative foods not only because the animals are forced to be less discriminating, but also because they are more susceptible to toxins.