Conditioned taste aversions: how sick must a ruminant get before it learns about toxicity in foods?

Abstract

Relatively little attention has been paid to the behavioural mechanisms that large herbivores may use to avoid being poisoned by toxins in plants. To determine if the food-avoidance learning abilities of large herbivores are as poorly developed as has previously been assumed, we investigated the relationship between the acquisition of a conditioned taste aversion (CTA) by sheep and the dose of gastrointestinal poison (LiCl) administered with a particular food. We also investigated feeding neophobia as a function of the LiCl dose associated with the previous novel food encountered. We found that the degree of CTA varied closely with the LiCl dose administered. A strong CTA was induced with 150 mg LiCl kg −1 body mass, which is similar to the dose required for a strong CTA in rats. We also found that feeding neophobia among sheep increased as a function of the LiCl dose associated with the last novel food encountered. When sheep and goats were offered food containing 2% LiCl, their daily intake after the third day fluctuated about a level that resulted in a LiCl dose of 39 mg kg −1 for sheep and 27 mg kg −1 for goats. These dosages are not much higher than that which causes mild discomfort in humans. We conclude that the food-avoidance learning abilities of ruminants are better developed than was previously assumed, and that CTA behaviour could be an important means by which large herbivores reduce the risk of being poisoned while foraging.