- Food value of Karoo shrubs. Part 5
|Last update: April 5, 2012 08:50:40 AM|
FOOD VALUE OF KAROO SHRUBS
E. E. BUTTNER
SKAAPBOSSIE, GROOT GANSIE, GOEIE KAROO (Pentzia Incana)
This is one of the dominating plants on non-brak soil of good farms where sheep are known to get fat rather than develop more flesh. In fact some farmers even complain that on veld with mostly Skaapbossie their sheep get too fat without sufficient flesh to balance the fat. While the carrying capacity of the shrub for sheep per morgen is fair, its effect on the body weight is better than that of most Karoo shrubs except, of course, for plants like Old Man Salt Bush, Woolly Finger Grass, and Rivierganna, which produce the highest gains in body weight where they dominate the veld.
Just why the shrub should be so fattening is not easy to say from the chemical composition. It is true, however, that the carbohydrate content is by no means low, but there are other shrubs with a higher carbohydrate content but which are less fattening. We can understand why the shrub is not a flesh-builder because its protein content is on the low side, ranging from about 7 to 16 per cent., according to the season. And its mineral content is also on the low side for a Karoo shrub but still higher than the values found in our best veld grasses. The phosphate content, too, is by no means high, but the outstanding feature of the mineral content is its low value for magnesium. This is perhaps the reason why the shrub causes paralysis (bewerasie) in horses, which require more magnesia per unit of body weight than sheep do. On the whole, the mineral content of the shrub seems to approach that of a good pasture grass.
This also applies to the organic compounds like protein, fibre, etc. Of course, the value of a plant does not only depend upon its food value but also upon its dietetic value. For example, certain shrubs contain certain trace minerals poorly represented in others but which are of vital importance under the conditions prevailing in the area. Then, too, some plants are especially rich in certain vitamins that are vital for that particular area. Certain essential oils, too, play an important part in the dietetic value of the diet and have a strong aroma.
Skaapbossie cannot stand overgrazing well because it results in the usual high bush with spare green twigs. Grazed veld in times of drought never gives the impression of a green plot. The reason is probably that the sheep only eat the leaves and ignore the bare bush. The plant would, however, shoot out again if the twigs were eaten too, the same as would occur if it were cut regularly. Controlled grazing will however, produce almost twice as much edible material per year per morgen as will occur in uncontrolled grazing, at least during the best time of the season.
Among the Pentzias there are several varieties, however. Some of them are even grazed very sparingly, if at all. The one known as Groot Gansie, a large-flowered variety, is perhaps one of the best grazed of the lot. It is a vigorous grower and may reach a height of twelve inches or more. Experiments have shown that Groot Gansie at its best is but slightly inferior to lucerne hay in digestible protein. As regards the digestible nitrogen-free extractives (carbohydrates) the plant is even superior to lucerne hay. Its starch equivalent is also higher. But the value for digestible crude protein was found much lower than for lucerne hay. In the pre-flowering stage, Pentzia was found superior to lucerne hay in feeding value, for it supplies almost as much digestible protein and is much superior in the energy-producing nutrients.
Pentzia Incana thus lends itself well to the use of localities rich in brak water, or where the boreholes are rich in common salt, or where salt licks are necessary, because the shrubs do not cause salt excesses when eaten heavily.
Another feature of the plant is its relatively low moisture content, even during the wet seasons. By not absorbing much water the plant seems to strive to keep its content of brak salts down, hence its preference for non-brak areas. Sheep suffering from excess of brak veld would do well to graze on Skaapbossie for a time to enable them to recover their physiological balance again.
In some years the highest protein content is found from the months of February to May. The moisture content varies little during the entire year, however, at least as far as the edible portion is concerned. The phosphorus content seems to run parallel with the protein content and is also at its best during the same months as is the case for protein. Few Karoo shrubs are so low in potassium and sodium, which makes this shrub valuable for sheep suffering from alkalosis or excess of brak environment.
Owing to the fattening properties of Groot Gansie, its effect on the fleece is to make it greasy, but this is again compensated for by the fact that such wool contains less suint, owing to the low potash content of the shrub. The low protein content, however, tends to retard stimulation of wool growth, for wool is essentially a protein compound. Nevertheless, the shrub should make up for quality of wool what it lacks as regards quantity of wool.
Merino Breeders Journal 25 (1)