Food Value of Some Karoo Shrubs
E. E. BUTTNER
THIS is one of our best natural sources of protein for sheep. Firstly the protein content is fairly high, and secondly it remains fairly constant throughout the year, as compared with most other Karoo shrubs. Its fat content too is fairly high, as compared with many other shrubs. Experience has shown that Vaalbrak produces the greatest increase in body weight and fat when grazed to any considerable extent for some time. The plant is very rich in common salt, and contains more phosphorus than many other shrubs. Any plant with a good supply of phosphorus is most valuable in South Africa, where phosphorus deficiency is an over recurring problem in the natural grazing. This and protein, plus certain trace elements and vitamins are the most essential nutrient elements for our grazing animals during most of the year.
Vaalbrak is of course also fairly rich in lime, magnesia, potash and silica, as is generally the case with the soil and water in many Karoo areas. It is thus clear that licks rich in common salt are not required in these parts, because an excess of salts tends to keep the bowels too open and reduce the digestibility of the food. A high silica content is an advantage because of its favourable effect on the quality and growth of the woo fibre, lending resilience and elasticity to the fibre, increasing its powers to withstand rough handling.
Unfortunately no research work on the trace mineral content of our Karoo shrubs has yet been published so we cannot tell at present just what elements are most essential to add to a lick where the animals get plenty of Vaalbrak feed. Nor do we know which trace elements are in excess. Yet it is important to have all this information before we can work out a really good lick or supplement for times of drought and feed scarcity. When adding trace elements it is most essential to avoid any excesses or incorrect proportions because these elements are very potent factors in the health of the animal, either for good or for bad, especially in certain inorganic forms.
This valuable plant is also fairly rich in protein and phosphorus but varies somewhat during the course of the year. Unfortunately the shrub is rather rich in Epsom salt and Glauber’s salt, and thus tends to cause diarrhoea in sheep when grazed to any considerable extent. Unfortunately its potassium content is very high, which causes a state of alkalosis in the system, and this only aggravates the purgative effect of the magnesium and sodium sulphates. However, fed along with a good proportion of grass Klappiesbrak will produce good results, perhaps as good as those of lucerne feeding, at least as far as nutritive values are concerned.
The plant occurs in many parts of the Karoo .and is generally considered most excellent. Sheep graze it well during all stages of growth and during any time of the year. Unfortunately this has resulted in overgrazing of the shrub, so much so that it is becoming scarcer with the years. While the silica and chloride content is not low, it varies somewhat during the course of the year.
It may come as a surprise to be told here that Klappiesbrak contains as much protein, even digestible protein, as lucerne. But this is what the chemical analysis of the plant reveals. Feeding experiments on the digestibility of the shrub have borne out these findings. In fact experiments have shown that organic matter (protein, fat carbohydrates, fibre) is much more digestible in Klappiesbrak than in lucerne. The crude-protein fraction of the Karoo shrub of medium quality is equal to that of lucerne, while excellent quality Klappiesbrak is even somewhat higher than lucerne, as far as digestibility is concerned, especially for protein.
This valuable shrub has proved itself better in practice than its chemical analysis would lead one to believe, for its protein content is by no means high. At least the plant has proved better than its protein content would lead one to believe. But it may be that its high carbohydrate content more than compensates for its medium protein content. Numerous feeding experiments have indeed shown that an increase in the carbohydrates content of the feed results in a sparing action on the protein content. In other words a high carbohydrate diet places more protein at the disposal of the body for tissue formation, while a low carbohydrate content compels the body to use part of the protein for the production of energy and warmth leaving less over for tissue formation. In the case of Groot Gansie feeding, trials have shown that its digestible carbohydrate content is high, appreciably higher than that of lucerne (that is lucerne hay, of. course) for both plants were compared with each other in the dried state.
What is strange about this shrub is the fact that horses dare not graze it without getting paralysis (bewerasie), unless eaten only to a slight degree. But for sheep the shrub is even fattening. The strange thing is that the very properties of the shrub that fatten sheep cause trouble in horses. For the latter seem to suffer from excess carbohydrate (hyperglaecaemia, excess blood sugar) resembling sugar diabetes in humans. The fat content of the plant is quite good compared with other Karoo shrubs and this may contribute something towards its fattening properties.
Compared with lucerne this shrub contains about the same amount of digestible protein, more fat, and a higher starch equivalent, but less fibre. Owing to its higher carbohydrate content, the Karoo shrub is a good deal better than lucerne cut during the pre-flowering stage, at least as regards chemical composition, which does not, however, always work out correct in practice. The ash or mineral content of the plant is lower than that of any others, but its calcium content is nevertheless appreciable. The phosphorus content, unfortunately, is not high and varies quite a lot during the season.
Where the veld consists predominantly of this shrub, salt licks might in some cases be tolerably palatable to sheep, especially where the water is not too salty or brak. Probably the main reason why this plant fattens sheep is because it is not as laxative as many other Karoo shrubs, owing to the low Epsom salt and Glauber’s salt content of Groot Gansie. On the other hand it may not keep sheep as free from internal parasites as the more laxative shrubs.
Merino Breeders Journal 23 (4)