The mastic tree (Pistacia lentiscus) contains 20% tannins. The tree makes up 17% of the diet of Damascus goats, but only 6% of the diet of Mamber goats. Like many natural chemicals, tannins can be a toxin or a medicine depending on the dose. Mastic tannins can interfere with an animal’s nitrogen balance but also can act as a de-wormer.
Researchers in Israel examined how readily young goats infected with gastro-intestinal parasites ate mastic foliage. Goats with internal parasites typically have a decrease in plasma cell volume value and a decline in growth rate. Mamber and Damascus goats were infected with internal parasites and then fed either hay or hay and mastic foliage.
Fecal egg counts declined sharply in goats that ate mastic foliage compared to the hay diet, but it also impaired the protein balance of the goats, determined by a decrease in blood urea levels.
When given a choice between hay and mastic, infected mamber goats ate 14% more mastic than non-infected Mamber goats. Damascus goats ate the same amount of mastic whether or not they were infected with parasite. Infected goats fed hay, regardless of breed, increased intake of mastic when given a choice between the two feeds.
Goats can passively self-medicate provided they routinely eat high and constant amounts of masticate (tannins). Goats less likely to eat mastic, such as Mamber goats, eat more of the plant only when parasite load increased. Active self-medication can be explained by the neophilic (preferring novel foods) behavior of sick animals. Self-medication of parasite-afflicted goats is a complex process, involving previous foraging habits affected by breed and experience.