Generally, leaves are more nutritious than stems and new leaves more valuable than old leaves. There are some exceptions to this generalization, especially when certain plant chemicals, such as tannins prevent proper digestion of the plant tissue. The total effect of these binding chemicals on the nutritional values of plants are not fully determined, especially in many of the browse plants. 5 The Goat and Diet Selection Goats are agile and have exaggerated control of their mouth parts, allowing them to be very selective for diet. They are able to stand on their hind legs and climb rock cliffs and low growing trees to gain access to relished plants and plant parts that are unavailable to other livestock species.
Goats have a mobile upper lip, effective in nipping off plant parts very selectively.
As a result, the goat's diet is very diversified, consisting of small components of a large number of plant species. Very simplified vegetation, an all-grass meadow, for example, does not provide good nutrition for goats over a long period of time. Goats need access to a wide variety of plants in order to exercise diet selection, as different plants increase and decrease in nutritional value with seasonal changes. Many of the browse species have invaded or become overabundant in old, abandoned fields or on range and pasturelands following prolonged grazing by other livestock species. These invading species, collectively called ''brush'', often can be suppressed or eradicated using goats.