Self-medication with tannin-rich browse in goats infected with gastro-intestinal nematodes.

Primates self-medicate to alleviate symptoms caused by gastro-intestinal nematodes (GIN) by consuming plants that contain secondary compounds. Would goats display the same dietary acumen? Circumstantial evidence suggests they could: goats in Mediterranean rangelands containing a shrub - Pistacia lentiscus - with known anthelmintic properties consume significant amounts of the shrub, particularly in the fall when the probability of being infected with GIN is greatest, even though its tannins impair protein metabolism and deter herbivory. In order to test rigorously the self-medication hypothesis in goats, we conducted a controlled study using 21 GIN-infected and 23 non-infected goats exposed to browse foliage from P. lentiscus, another browse species - Phillyrea latifolia, or hay during the build-up of infection. GIN-infected goats showed clear symptoms of infection, which was alleviated by P. lentiscus foliage but ingesting P. lentiscus had a detrimental effect on protein metabolism in the absence of disease. When given a choice between P. lentiscus and hay, infected goats of the Mamber breed showed higher preference for P. lentiscus than non-infected counterparts, in particular if they had been exposed to Phillyrea latifolia before. This was not found in Damascus goats. Damascus goats, which exhibit higher propensity to consume P. lentiscus may use it as a drug prophylactically, whereas Mamber goats, which are more reluctant to ingest it, select P. lentiscus foliage therapeutically. These results hint at subtle trade-offs between the roles of P. lentiscus as a food, a toxin and a medicine. This is the first evidence of self-medication in goats under controlled conditions. Endorsing the concept of self-medication could greatly modify the current paradigm of veterinary parasitology whereby man decides when and how to treat GIN-infected animals, and result in transferring this decision to the animals themselves.