This idea that plants become desirable or aversive depending on their digestive consequences is simple. But, how do grazing animals figure out exactly which plants made them fee l good or ill? One way herbivores apparently accomplish this task is by regarding unfamiliar plants with caution. Animals associate positive or negative effects of nutrients or toxins with novel foods when offered meals that contain novel and familiar foods. When foraging bouts include several novel plants, plants that dominate the diet are probably 'weighted' more than less-consumed plants, even if the minor foods were primarily responsible for the positive or negative feedback. Furthermore, digestive feedback begins within 10 to 15 minutes of consumption which could help animals attribute digestive benefits or liabilities to specific plants. Finally, livestock grazing on rangelands usually become familiar with the forage resource and may seldom encounter truly novel plants. This allows greater opportunity to 'sort out' feedback from individual or similar groups of plants

When a grazing animal smells and tastes a plant, the flavor is either pleasing or distasteful depending on the animal's previous grazing experiences. When a plant is eaten, it provides feedback during digestion. If consumption of a plant improves the nutrient or energy status of the animal, the plant flavor becomes more desirable or pleasing. If eating of the plant yields illness, the flavor becomes aversive and distasteful (Fig. 2). These flavor-consequence relationships form the basis for dietary likes and dislikes, and the animal then seeks highly palatable foods and avoids aversive foods. The resulting behavior patterns generally lead to increased consump- tion of nutritious foods and limited consumption of toxic or low quality plants.

The digestive consequences of forage consumption are determined by plant forage quality and animal digestive and detoxification abilities. This interaction, in turn, affects the nutrients and energy available for animal growth and maintenance.

When an animal eats a plant, it receives digestive feedback in the form of energy, nutrients, illness, or toxicosis. If the feedback is positive, preferences are formed to the plant and if the feedback is negative, aversions are formed. The strength of the preference or aversion is determined by the magnitude, nature, and timing of digestive feedback