Discriminating among novel foods: effects of energy provision on preferences of lambs for poor-quality foods

Our objective was to better understand how lambs discriminate among novel foods based on flavor and post-ingestive effects. We first determined how temporal sequence of food ingestion and post-ingestive feedback affected preference when lambs were fed flavored wheat straw (a poorly nutritious novel food) immediately after eating mile grain tan energy-rich novel food), or after mile was infused in the rumen. Lambs did not acquire a preference for flavored straw when they were fed straw immediately after eating mile (P>.10), evidently because they quickly discriminated the flavor-feedback effects of mile from straw. However, lambs infused with mile prior to eating straw in one flavor or another preferred the flavored straw eaten after the mile infusions (P < 0.001), and they preferred mile > flavored straw eaten after mile infusions > flavored straw eaten without mile infusions (P < 0.001). Thus, when the flavor cue (milo) was removed, lambs did not discriminate milo from straw to as great a degree as when they first ate mile and then ate straw. We next attempted to better understand how lambs quickly discriminated between novel foods - grape pomace-starch (70-30%) and grape pomace-cellulose (70-30%) - that differ in digestible energy content. Lambs preferred pomace-starch from first exposure (P < 0.001), and we hypothesized that they generalized a preference from eating familiar foods like barley and mile that are about 80% starch to the novel grape pomace-starch mixture. To test this hypothesis, we gave lambs a toxin (LiCl) dose after they ate mile, and then measured their preference for pomace-starch. Intake of pomace-starch was lower in the Milo-LiCl group than in controls that received only LiCl (P < 0.001), which is consistent with the hypothesis that lambs generalized a preference from familiar foods (barley and mile) to a novel food (pomace-starch). Finally, we determined how duration and amount of exposure to two novel foods - grape pomace-starch (70-30) and grape pomace (100) - influenced preference. When both foods were offered for only 20 min/day, intake of pomace and pomace-starch did not differ on day 1 to 8, and pomace was preferred to pomace-starch during day 9 to 15 (P < 0.05). This pattern quickly reversed - pomace-starch became preferred to pomace - when the foods were offered for 8 h/day for the next 6 days (P < 0.001). These findings suggest that energy deprivation and the amount of food ingested both affected how quickly lambs discriminated between foods that differed in energy, and that lambs needed to eat a threshold amount of an energy-rich novel food before they acquired a preference for that food. (C) 2000 Elsevier Science B.V. All rights reserved.