Food aversion learning in lambs with or without a mother: Discrimination, novelty and persistence

Abstract

The livestock industry suffers substantial losses from animals eating poisonous plants. Research on learned food aversions will enhance understanding of the abilities of livestock to detect and avoid toxic foods. This study sought to determine: (1) whether lambs and ewes can be aversively conditioned to avoid palatable foods; (2) whether learned aversions persist; (3) whether aversive conditioning affects how lambs and ewes respond to novel food; (4) the influence of the mother on the lambs' learned food aversions. The results clarified several points. (1) The treatment group of sheep learned to avoid rolled barley (RB) and rabbit pellets (RP) containing 2% lithium chloride (LiCl), a non-lethal gastrointestinal poison. However, they always sampled small amounts of RB and RP that contained LiCl, and increased consumption when foods no longer contained LiCl. Conversely, the control group of sheep accepted RB and RP containing 2% sodium chloride (NaCl) and increased the amount ingested during each exposure. Alfalfa pellets, the basal diet, were consumed readily and entirely by treatment and control groups throughout the study. (2) Learned aversions persisted for at least 60 days. (3) Treatment and control animals ingested small amounts of RB and RP when they were novel foods. Poisoning made ewes and lambs, but not orphans, more neophobic than unpoisoned sheep. Ewes spent less time at food boxes than lambs, suggesting that poisoning made ewes more neophobic than lambs. (4) Lambs separated from their mothers spent less time at food boxes than orphaned lambs, but both groups ate the same amount. That sheep learned about the consequences of ingesting foods and that they remembered for at least 60 days is evidence that diet selection can be manipulated. If sheep have an inherent tendency to sample noxious feeds, however, they will avoid particular foods only if they are always noxious. Conversely, if the sampling behavior of sheep was an artifact of the procedures and sheep can be conditioned to avoid totally a particular food, it will be feasible to train sheep to avoid foods such as poisonous plants. Further research is necessary to clarify this aspect, to more fully elaborate the learning abilities of sheep, and to assess the implications for management.