Here is why:

The micro-organisms in the rumen can break down the material between the net venation of broadleaf plants more quickly than the material in parallel veined grasses. Since a goat has a rapid passage rate of material through its rumen, it needs to eat a plant that its rumen micro-organisms can break down quickly. Because the parallel venation in very young grasses is lower in non-digestible lignin, the micro-organisms in the goat's rumen can break them down rapidly too.The more mature grasses -- the grasses with the higher lignin content -- are harder for the goat's rumen micro-organisms to break down and process into nutrition. This does not mean that goats cannot eat grasses, but it does mean that goats need to eat young immature tender grass leaves -- leaves far less mature than cattle readily eat.

Broadleaf plants (forbs and browse) have their growing points at the top of the stems (apical dominance), which is why goats tend to eat the young tender growing parts of these plants at the tip of their stems. Goats eat the seeds of such plants because they are high in energy. Grasses, however, grow from the base of the plant (basal dominance), so the most digestible part of the grass leaf is the newer growth that comes from the ground level of the grass plant. And producers should remember that is also where the parasitic worms are that cause so much trouble with goat health.

Pasture Management and Re-Growth: Browsing of woody plants usually occurs at the end of the stems where the new growth is taking place. When these growth points are eaten, it takes more time and more nutrients to start new growth than grasses require to do the same thing. Continued feeding on lower new growth of browse plants is why browse lines on woody plants take so long to recover. When browse plants are continually eaten at a certain height, the plants tend to quit trying to grow new stems there and instead shift to other growth points higher up the plants which are less reachable for browsing. The is a survival mechanism for browse plants.

Because grasses grow from the base of the plant, they rebound and produce re-growth more quickly from grazing pressure than do forbs and browse. Continued re-grazing or grazing too close to the ground (where the crown point of the plant contains the buds needed for new growth) can cause trauma to the growth points and delay re-growth or deplete the nutrient reserves needed for re-growth. Over-grazing can cause the preferred plants in the pasture to die out and be replaced by less desirable and usually less nutritious plants. Noxious or toxic weeds will then begin to dominate the pasture because goats do not eat these plants.

To sum up: Stocking rates for goats are not based upon plant materials per acre available for consumption by goats. The producer must take into account the types of plant materials available that will provide the nutritional levels that goats need while giving them access to sufficient acreage to forage/browse over so that they can largely eat "from the top down" to avoid the internal parasites that wait for them on grasses near ground level.

This writer thanks Kent Mills, livestock nutritionist with HiPro Feeds, Friona, Texas, for his invaluable help in the preparation and editing of this article.

Suzanne W. Gasparotto
ONION CREEK RANCH
Lohn, Texas 12/8/09