Amount of experience and prior illness affect the acquisition and persistence of conditioned food aversions in lambs

We studied the acquisition of food aversions in sheep. In the first experiment, we investigated how prior illness affected the formation of a conditioned food aversion. Lambs were offered small amounts (< 200 g) of novel foods (wheat and rice) for 12 days, until lambs ate both foods readily. To establish an aversion to one of the foods, lambs were then given the toxin lithium chloride (LiCl) after eating one of the foods. On subsequent days, lambs were allowed to eat the food previously paired with LiCl until the aversion extinguished. When lambs later consumed a meal of wheat and rice and received LiCl, they avoided the food that had been paired with LiCl, but they did not reduce intake of the other food (P < 0.001). In the second experiment, we examined how amount of experience with a food affected the acquisition and persistence of a food aversion. Lambs were offered oats (novel food) at 1% body weight for either 28, 14, 7, or 1 days. An aversion was then induced by offering oats followed by LiCl. Lambs with at least 14 days exposure to novel foods formed the least persistent aversions (P = 0.002). Furthermore, the aversion to oats extinguished within 6 days in lambs offered oats for 7 days. Thus, lambs are not likely to abstain from a food they were trained to avoid (e.g. trees in orchards, poisonous plants) if they have more than 7 days experience with the food. Finally, lambs should be fed small amounts of highly nutritious novel foods (e.g. grains) during the first 7 days to avoid gastro-intestinal distress and more persistent aversions.