LEAF VENATION  AND  HOW  IT  AFFECTS  GOAT  NUTRITION

Goats as a species are herbivores, i.e.  plant-eating animals.   Goats are ruminants, and ruminants are animals that  partially chew their food before they swallow  it into their rumen, which is the largest of their four stomachs,  then   regurgitate it for further processing  by chewing their cud.

Goats have the fastest metabolism of all ruminants (except deer),  which means that they must eat several times a day  and need to have a higher quality of plant material than other ruminants in order to thrive.  Goats are very selective eaters, using their prehensile mouth (lips and tongue) to choose the tastiest plants.  As a percentage of body weight, goats eat a larger volume of plant materials than cattle eat.

Goats get their nutrition through the use of their highly-adapted teeth, mouths, and digestive systems to break down  the cell walls in leaves.   Leaves are primarily comprised of cellulose, a complex carbohydrate that supports the plant's cell walls, and lignin, which is the chief non-carbohydrate part of the plant that binds with cellulose to harden and strength cell walls.  Lignin is in the vein structure of plant leaves as well as in the stem to give the plant enough rigidity to stand upright and compete for sunlight.  The function of the veins is to act as a conduit for water and nutrients from the soil and transport the products of photosynthesis to other parts of the plant. The cell contents within the cell walls are the most digestible parts of the plant.

There are two types of vein structures in plant leaves: net and parallel venation.  Broadleaf plants, forbs, and browse have net venation.  The only forbs that have parallel venation are those that are "grass-like" members of the lily family.   All grasses have parallel venation.

Here is why goats do best eating forage and browse:  Net venation leaves are easier for goats to break down because the material between the veins is the more digestible part of the leaves.  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 more quickly.   Because the 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 (browse and forbs) 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 many 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.

Suzanne W. Gasparotto, ONION CREEK RANCH   11.1.21

The author, Suzanne Gasparotto, hereby grants to local goat publications and club newsletters, permission to reprint articles published on the Onion Creek Ranch website under these conditions: THE ARTICLE MUST BE REPRODUCED IN ITS ENTIRETY AND THE AUTHOR'S NAME, ADDRESS, AND CONTACT INFORMATION MUST BE INCLUDED AT THE BEGINNING OF THE REPRINT. We would appreciate notification from any clubs or publications when the articles are used. (A copy of the newsletter or publication would also be a welcome addition to our growing library of goat related information!)

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