agricultural production guidelines
m
Veld in KwaZulu-Natal
Co-ordinated Extension KwaZulu-Natal Veld 9.6 1999
USE OF BROWSERS AND LICKS IN GRAZING MANAGEMENT SYSTEMS
J M B Smith
KwaZulu-Natal Department of Agriculture
INTRODUCTION
The provision of supplementary licks and the use of browsers can be useful management tools which assist in the optimum utilization of the vegetation by livestock.
To make optimum use of the vegetation in the arid savanna areas of Bioresource Groups 21, 22 and 23, the browsing animal such as the goat should be introduced. Greater production could be obtained from this veld type by using a combination of grazers and browsers, than by using grazers alone. While it is true that the production of browse is usually significantly lower than that of grass, it has the advantage of being less variable both within and between seasons. It is therefore a source of forage which should not be ignored.
The majority of savanna trees and shrubs have a terminal growth habit, and the dormant buds situated at the base of the stem will develop only if the apical dominance of the aerial parts is removed (refer to Production Guidelines 7.3 and 7.7 in this series). The destruction of the apical growing point of the twig usually leads to a spectacular increase in twig production, but, if applied too severely, or too frequently, it can be damaging to the bush species. Continuous heavy stocking with goats will result in a gradual mortality of trees and shrubs. Alternatively, correct stocking of goats in a rotational browsing system can lead to the maintenance and optimum use of the bush. The objective must be clearly defined in decisions on goat management (i.e. whether the intention is to reduce the bush density for cattle, to maintain the bush for goat production, or to utilize the veld for both cattle and goats). This will depend on the relative profitability of the different enterprises, and, to a certain extent, the vegetation type. For the sake of convenience, the savanna vegetation is considered under two major groups for the purposes of examining the potential of browsers in KwaZulu-Natal. The Thornveld regions represent those savanna areas which are dominated by plants with spines, particularly the acacias. The Valley Bushveld represents the savanna vegetation found in the major valley systems south of the Tugela river, and in which broadleaf plants are more common.
In the eastern Cape it has been found that grass yield is affected by tree density only when this increases beyond 1 000 tree equivalents/ha. (A tree equivalent (TE) is taken as a woody plant 1.5 m in height. Thus a woody plant of 4.5 m is equal to 3 TE, having 3x the competitive effect on grass production as a tree of 1.5 m height - refer to Production Guidelines 2.4 and 2.5 for more detail). At 1 500 and 2 000 TE/ha, the grass yield is reduced by 40% and 60%, respectively. For maximum forage production from a combination of grass and bush, tree density should be maintained at about 1 000 TE/ha.Thornveld
Sweet thorn (Acacia karroo), the dominant tree in this veld type, is sensitive to browsing during the early growing season, and should receive only a light defoliation of about 25%, followed by a rest period of 180 days. To reduce the browsing stress during this time, goats should be spread over the whole farm, or move rapidly through the camps, for the first two weeks of the growing season. During the rest of the season, trees should be defoliated to about 50% to 75%, followed by a 100-day rest period. The browsing capacity should be based on 2 000 browse units. A browse unit is defined as a tree or shrub with browsable herbage within a height of 1.5 m (refer to Production Guideline 2.4 of this series for greater detail on determining browse units). The stocking rate should be one goat to one or two hectares, depending on the bush density. This ensures that goats will consume a minimum of grass.
The cattle stocking rate will depend on the amount of grass present and the bush density, and should be light enough to ensure that browsing by cattle is minimised. Only half of the available grass growth should be utilized at any time during the growing season. Assuming cattle require 3 500 kg of dry matter per annum, an area producing 700 kg of grass and having 1 000 trees per hectare should be able to support one cattle AU and six goats per 10 ha.
Cattle and goats should move through the camps in two separate rotations. For cattle, the period of stay should be 7 to 14 days, with a period of absence of 60 to 90 days. For goats the period of stay should be 14 to 21 days and the period of absence 100 to 180 days. To encourage vigour in degraded veld, one-third of the area should be rested each season for 12 months, from July to June. No additional rest would be required for the woody component.
The number of camps required would be 6 to 9 per group, but preferably 12 camps for degraded veld, to ensure that one third of the camps are rested. In KwaZulu-Natal, where a variety of acacias (as opposed to one species) occur in the Thornveld, the basic principles of utilization would still apply, but the norms would have to be modified accordingly.
Valley Bushveld
In the eastern Cape, the woody component in veld which is in good condition would normally have a density of between 2 000 to 3 000 plants per hectare. The main grasses are redgrass (Themeda triandra), and species of Panicum and Digitaria.Valley Bushveld in good condition contains spekboom (Portulacaria afra) as one of the dominant trees. Leaf and shoot development in this tree is stimulated by moderate defoliation in summer and autumn. Therefore a moderate defoliation (40 to 50%), followed by an adequate rest period, is recommended at these times. However, defoliation during winter has a depressing effect on growth, and so as much resting as possible is advisable in winter, particularly in areas in which spekboom has low vigour.
Recommended periods of stay and absence for a 12 camp per flock system during various times of the year are presented in Table 1. Because the veld is generally in a degraded condition, a resting programme should be introduced. After summer browsing, which stimulates twig growth, a 15-month rest period should be provided. Autumn browsing improves leaf growth, and should be followed by a 12-month rest. This resting programme should be provided, outside the normal browsing rotation, to any camp or set of camps which require production to be increased.
The growth of grass is very dependent on the rainfall. Grasses flush after rain and then remain dormant until the next rain. Long periods of absence are therefore advisable during the growing season. Certain camps should be rested to accumulate forage for the inevitable dry spells.
To achieve this, one third of the camps should rest from August to mid-December, for use in late December, January and early February. For winter use, a further one-third of the camps should be rested from late February to May. The herbaceous layer which is not being rested should receive a 60- to 90-day period of absence, with a period of stay of 7 to 14 days. To achieve this, it becomes necessary for cattle and goats to move through the same set of camps in two different rotations.
Table 1. Periods of stay and absence recommended for a 12 camp goat management system.
|
Period of stay (days) |
Period of absence (days) |
Season |
|
9 7 3 20 |
105 84 30 224 |
Spring Summer Autumn Winter |
In assessing stocking rates, approximately 1 500 browse units of 1.5 m high are required per goat. Valley Bushveld in good condition would support 6 goats (1 AU) per 6 ha. Where the herbaceous component is dominated by species of Digitaria and Sporobolus, the stocking rate should be reduced to 6 goats per 12 ha. In very poor veld, the stocking rate would be 6 goats per 24 ha. The cattle:goat ratios would vary according to the amount of grass available, and the condition of the veld.
The Valley Bushveld in KwaZulu-Natal has very limited, if any, spekboom, and differs in species composition from the valley systems occurring in the eastern Cape, and although the same principles of utilization apply, research is required to set modified parameters.
The utilization of veld can be improved through the application of sound veld management principles, together with the judicious use of supplementary feeding. In the sourveld areas, growth in early summer is very vigorous and the herbage is rich in protein (approximately 10%), adequate in carbohydrates and low in fibre. During this time, animals have a high growth rate, which could lead to a shortage of phosphorus, and therefore supplementation with phosphorus is generally advisable. As winter approaches, the crude protein content of the grass declines steadily to about 4% in mid-winter. This is accompanied by an increase in crude fibre from about 32% to 37%. As a result, the digestibility of grass declines from approximately 65% to 40%.
With the decline in digestibility of the organic matter, the movement of ingested material through the digestive tract slows down. This results in a lower rate of intake by the animal. Intake is reduced by as much as 50% from the beginning of summer to mid-winter (e.g. from 10 kg to 5 kg dry matter per day per AU). These effects can be lessened or eliminated by supplementing the animal's diet with protein.
In winter, the digestibility of protein in grass in sourveld areas declines to a negative value, and protein supplements are required once the crude protein level of grass drops to about 5%. These supplements are able to increase the digestibility of cellulose in the grass from about 40% to 80%, with a resultant increase in the rate of passage of the ingested material through the digestive tract, and an increase in the consumption of dry grass.
During autumn and winter in the sourveld there is usually an abundance of dry grass which is sufficient for the animals' requirements. The phosphorus and carbohydrate status is adequate, due mainly to the reduced growth rate of the animal. Normally, therefore, phosphorus and energy supplementation are not necessary at these times.
In general, it can be concluded that supplementary feeding resolves itself into supplying extra phosphorous in summer and protein in winter. In very cold areas, where frosts are frequent, extra energy may also be required in winter. Supplements will induce animals to utilize more grass which, in turn, will tend to alleviate the problem of removing top hamper by burning or mowing.
In the sweetveld areas, e.g. Bioresource Groups 21 and 22, the grazing remains palatable for a much longer period than in the sourveld. In addition, animals augment the protein in their diets with browse, which has a crude protein content varying from 7% to 15%.
Therefore protein supplements are seldom required in these areas.
Suitable supplements can take the form of meals, licks, cubes or blocks. These should be placed away from water points to encourage animals to increase their range of grazing. Old grass can be removed or trampled to form litter by concentrating animals artificially by moving licks to areas of moribund grass.
LITERATURE CONSULTED
AUCAMP, A.J. & TAINTON N.M. Veld management in the Valley Bushveld of the eastern Cape. Bulletin number 401, Government Printer, Pretoria.
TAINTON N.M. (ed.). 1981. Veld and Pasture Management in South Africa. Pietermaritzburg : Shuter & Shooter.
TROLLOPE, W.S.W. 1980. Controlling bush encroachment with fire in the savanna areas of South Africa. Proceedings of the Grassland Society of Southern Africa 15 : 173 -177.