HOW GOATS LEARN TO DISTINGUISH BETWEEN NOVEL FOODS THAT DIFFER IN POSTINGESTIVE CONSEQUENCES

To better understand some of the mechanisms that control selection of novel foods differing in postingestive consequences, we offered goats current season's (CSG) and older (OG) growth twigs from the shrub blac kbrush (Coleogyne ramosissima). CSG is higher than OG in nitrogen (1.0 4% v. 0.74%) and it is more digestible in vitro in goat rumen fluid (4 8% v. 38%). Nevertheless, goats acquire a preference for OG because CS G contains much higher levels of a condensed tannin that causes a lear ned food aversion. When CSG and OG were offered to goat naive to black brush, the goats did not choose either OG or CSG exclusively, but when they finally (1) ate more CSG than OG within a meal (averages of 44 g and 16 g, respectively) and (2) ate enough CSG within the meal to acq uire an aversion (average of 44 g), they ingested less CSG than OG fro m then onward. Accordingly, the change in food selection resulting fro m postingestive feedback was influenced by the amount of each food ing ested within a meal. This was further shown when we varied the amounts of CSG and OG that goats ingested within a meal, and then gave them b y gavage the toxin lithium chloride (LiCl). They subsequently ate less of the food eaten in the greatest amount, regardless of whether it wa s CSG or OG. The salience of the flavor (i.e., taste and odor) of CSG and OG also played a role in the acquired aversion to CSG. Salience ev idently was due to a flavor common to both OG and CSG that was more co ncentrated in CSG. We conclude that the relative amounts of different foods ingested within a meal, and the salience of the flavors of those foods, are both important variables that cause goats to distinguish b etween novel foods that differ in postingestive consequences.