• Behavioral toxicology of livestock ingesting plant toxins

      Pfister, J. A.; Cheney, C. D.; Provenza, F. D. (Society for Range Management, 1992-01-01)
      Traditionally, effects of plant toxins on livestock have been measured using tissue or biochemical changes to determine the extent of intoxication. In addition to traditional approaches, toxic effects can be measured using behavioral principles; this discipline is called behavioral toxicology. Behavioral toxicology is a combination of toxicology, pharmacology, and the experimental analysis of behavior. Behavioral toxicology offers a sensitive means to determine toxic impacts by evaluating behavior, since behavior is a functional integration of all body systems. Concurrent use of behavior and traditional pathological measures will enhance our understanding of plant-caused intoxications. Operant analysis of animal behavior is a powerful technique used often in behavioral toxicology for establishiig normal behavior, and detecting toxicity-induced deviations from normal behavior. Behavioral toxicology can provide an understanding of ingestive and reproductive (sexual and maternal) responses of livestock after exposure to a variety of plant toxins. Such information, together with knowledge about plant/animal interactions, will provide range and animal managers with tools to use in preventing or reducing livestock losses to poisonous plants.
    • Mechanisms of learning in diet selection with reference to phytotoxicosis in herbivores

      Provenza, F. D.; Pfister, J. A.; Cheney, C. D. (Society for Range Management, 1992-01-01)
      Our objective is to develop explanations for why herbivores ingest poisonous plants by first discussing how herbivores learn to select diets, by then considering mechanisms that enable herbivores to ingest phytotoxins, and by finally developing hypotheses about why herbivores overingest phytotoxins. Animals learn about foods through 2 interrelated systems: affective and cognitive. The affective system integrates the taste of food and its postingestive feedback; this system causes changes in the intake of food items, depending on whether the postingestive feedback is aversive or positive. The cognitive system integrates the odor and sight of food and its taste; animals use the senses of smell and sight to select or avoid specific food items. We further divide cognitive experiences into 3 categories: learning from mother, learning from conspecifics, and learning through trial and error. Physiological and conditional responses enhance the ability of animals to ingest phytotoxins. Physiological mechanisms include binding the compound before it can exert its action, metabolizing the compound so it cannot exert its action, and tolerating the compound. Conditional responses complement physiological responses and further decrease herbivore susceptibility to toxins by preparing the animal for the effects of the toxin. Herbivores are likely to overingest poisonous plants when any of the aforementioned systems fail. For example, the affective system is likely to fail when phytotoxins circumvent the emetic system, when aversive postingestive consequences are delayed temporally and positive consequences during the delay are pronounced, and when toxicosis is accompanied by a change in environmental context. Likewise, cognitive systems are likely to fail when animals are unable to distinguish subtle molecular changes that render nontoxic plants toxic, when toxins in 2 or more plants interact, and when herbivores are unable to differentiate nutritious from toxic plants as a result of being placed in an unfamiliar environment. We conclude that a thorough understanding of affective and cognitive systems, and the specific conditions under which these systems fail, will be necessary in order to understand why herbivores ingest foods that do them harm.