Last update: April 5, 2012 09:32:47 AM E-mail Print

 

FOOD VALUE OF SOME KAROO SHRUBS

E. E. BUTTNER

 

THIS well-known sheep feed is fairly rich in protein, carbohydrates, and minerals, but is by no means one of our richest fodder plants. Unfortunately the fibre content is also rather higher than is the case with a few other Karoo shrubs eaten by sheep. However, this is not a serious obstacle when the plant is still green and fresh. Green Karoo shrubs are of course also sources of various vitamins, enzymes (ferments) and other organic compounds of greater or lesser value, but these have not been studied sufficiently as yet. Nor do we know much about the biological value of the proteins of the Karoo plants, except that the value is high in green plants when fresh and young.

Of the minerals, potassium ranks highest, as usual in green plants. But sodium is almost as high. While some of the potassium and sodium is in the form of chloride, most exists as sulphate. This means that most of the minerals are in the form of. Glauber's salt and common salt (sodium chloride). Both potassium and sodium chlorides have the same taste, namely that of table salt. This explains why sheep are so fond of Karoo shrubs like Rivierganna and others with high chloride content. From this we see that sheep eating fair amounts of Rivierganna do not require any salt in their licks or supplemental feeding. This only becomes necessary when the salt-bearing shrubs are scarce. Yet many provide their sheep with licks rich in salt and bone meal, or salt and phosphates. It is true that phosphate supplements are always necessary even when the Karoo veld is green, because the calcium and magnesium content of Rivierganna and other Karoo shrubs is rather high, so much so that they tend to render the phosphates in the plants less available than is the case with grasses and cereal fodders. Another factor that tends to render the phosphates less available is the great excess of base forming salts over the acid-forming ones, even though a certain degree of excess is normal for sheep, because a base-forming diet enables the animal to make its protein supplies go further than an acid forming one would. Unfortunately, however, Rivierganna is rather rich in magnesium sulphate, which is of course nothing else than Epsom salts. This together with the high content of Glauber's salt tends to make Rivierganna rather laxative. Now we can understand the common experience of sheep farmers where this plant grows, namely that it does not fatten sheep at all. In fact the animals grazing on it, either to a great extent or on little else, are only just able to maintain their bodyweight, even though eating plenty of the shrub. Still, the carrying capacity of the shrub is high, i.e. about 2¾ sheep per morgen on the average on some farms. This ranks amongst the highest figures of any of our Karoo shrubs so far studied. In a mixed veld this shrub is grazed right down to the ground, but on veld where it predominates or exists alone sheep do not favour it much, probably because it is too salty by itself, or because it increases the need for phosphates, or because of its high content of sulphates. On the other hand its laxative properties would tend to keep worms down. Farmers have often told me that sheep removed from grassveld to Rivierganna veld, lose most of their internal parasites.

During November to January the protein content of this valuable shrub is just as high as that of Rivierganna but does not fall so low during the rest of the year. Its mineral content, however, is about twice as high. But unfortunately this is due to its higher sodium chloride (salt) and Glauber's salt content, while its Epsom salts content is about as high. In fact its sodium chloride content is extremely high so that the plant has been given the correct name. Salt licks where sheep consume much of this plant are therefore not only superfluous but may even be more or less harmful. I have been told by farmers with large areas of this shrub that they cannot induce their sheep to take salt licks, even during a drought with little feed. But phosphate supplements are nevertheless required to raise the phosphorous content of the diet to a more favourable ratio. As with other fodder plants Karoo shrubs vary considerably in their chemical analyses during the course of the year but their phosphorous content never falls as low as that of our grasses in winter. Unfortunately in areas where Karoo shrubs grow well the water is also brak and rich in just the same salts as the shrubs are already excessive in. This helps to aggravate the position as regards phosphorous requirements and the palatability of licks with salt. In these cases only the water-soluble phosphates should be given, especially disodium and mono-ammonium phosphates, which tend to improve the acid-base position of the diet, at least in so far as the brak water does not precipitate the phosphate and render it less available in the body.

As climatic conditions during any given month are not the same every year we must allow for the fact that from October to December, the Glauber's salt content of Karoo -shrubs may be at its highest in one year, and in another year the same will be true for the months of September to January. It may even occur that the Epsom salts content may be at its highest during May in certain years.

 

Published

Merino Breeders Journal 23 (3)