In contrast to other farm animals, except llamas, goats prefer shrubs and tree leaves, whether deciduous or evergreen. Because of this preference, goats have been used to control encroaching shrub-type growth in pastures. Goats consume approximately the same weight of forage as do sheep of similar size. Goats tend to select highly digestible portions of most forages and show a preference to browse along fence lines and rough areas. Goats usually perform on improved pastures and prefer browse to grass (a diet of >80% browse).
Browse (leaves and twigs of trees and shrubs) generally contain higher levels of crude protein and phosphorus during their growing season than do grasses. However, some palatable browse species are limited in value because of one or more inhibitors that may bind or otherwise prevent use of nutrients contained in the plants. One such inhibitor is lignification of woody twigs and tree leaves, which physically binds (or encapsulates) the desirable nutrients. Certain plant-based oils (terpenes) are present in some range shrubs and apparently inhibit growth of rumen bacteria but may have positive effects on internal parasite control.
High concentrations of tannins are present in certain browse plants and depress digestion of feedstuffs by binding enzymes or by inhibiting enzymatic activity. Excessive tannins may also increase sulfur requirements, which may be more critical for hair-producing goats. However, in spite of these potential problems, when given the opportunity to choose, goats appear to be able to select more digestible and beneficial browse. Grazing or browsing tannin-containing plants may help control many species of internal nematode parasites.