Sheep self-medicate when challenged with illness-inducing foods

People learn to take aspirin for headaches, antacids for stomach aches and ibuprofen to relieve pain, and often obtain prescriptions from doctors for medications. Is it also possible that herbivores write their own prescriptions? From prehistoric times, people have looked to the presumed self-medicative behaviour of animals for remedies of ailments but it is still not clear whether animals seek medicinal compounds to recuperate from illness. Evidence of self-medication is based almost exclusively on observations rather than experimental analyses. We examined whether lambs select specific protective chemicals to recuperate from ingesting malaise-inducing foods. In pen studies, lambs in a treatment group were conditioned to consume foods and toxins (grain, tannins, oxalic acid) that led to negative internal states and then allowed to eat a substance known to attenuate each state (sodium bentonite, polyethylene glycol and dicalcium phosphate, respectively). Control lambs ate the same foods and medicines, but disassociated temporally, so they did not recuperate from illness. After conditioning, lambs ingested grain or food with tannins or oxalates and then received a choice of the three medicines. Only the treatment animals preferred to eat the specific compound known to rectify the state of malaise induced by the food previously ingested. Control animals never changed their pattern of use of the medicines, regardless of the food consumed before the choice. This first demonstration of multiple malaise–medicine associations supports suppositions in zoopharmacognosy and current hypotheses of homeostatic endeavour, and has implications for the well-being of wild and domestic animals.