agricultural production guidelines
m
Veld in KwaZulu-Natal
Co-ordinated Extension KwaZulu-Natal Veld 9.7 1999
VELD MANAGEMENT AND SHEEP PRODUCTION IN SOURVELD
M B Hardy
Western Cape Department of Agriculture
Growth
Pattern and Nutritional Value of Sourveld
Sheep Grazing Habit
Veld Management
for Sheep Production in Sourveld
Cattle-to-Sheep Ratio
INTRODUCTION
Sheep production systems based on veld in KwaZulu-Natal are confined largely to the high elevation sourveld vegetation types. The sourveld occupies the western and central portion of KwaZulu-Natal and comprises the foothills and eastern slopes of the Drakensberg range, from Kokstad in the south to Paulpietersburg in the north (Bioresource Groups 8, 9, 11 & 14). Elevation ranges from approximately 950 m to 2150 m above sea level.
The sourveld is dominated by a short, dense grassveld and may be divided into two broad phases based on rainfall. Generally, the drier phase occurs in an area around Kokstad, Cedarville and Matatiele in the south and along the Free State and Mpumalanga border in northern KwaZulu-Natal. The remaining parts of the sourveld are moister grasslands and receive, on average, approximately 150 mm more rainfall than do the drier areas. Extensive sheep production systems are mostly confined to the drier areas of sourveld.
GROWTH PATTERN AND NUTRITIONAL VALUE OF SOURVELD
By definition, sourveld is veld in which the forage plants become unacceptable and less nutritious on reaching maturity. The veld is thus suited to grazing for only a portion of the year. As the season progresses, the typical nutritional pattern of grasses in sourveld through the season is one of high nutrition and high palatability of new growth during spring and early summer, after which there is a rapid decline to low nutrition and low palatability in the late summer and autumn. After the first severe frosts, the nutritional value of the grasses is extremely low and few classes of livestock are able to show mass gains, or even to maintain mass, on this source of feed during winter.
Plant growth commences in spring when temperature and moisture conditions are favourable for such growth. Since the rainfall pattern in the drier phase of these sourveld areas varies considerably from year to year and from season to season, plant growth could start as early as September or as late as November. Once growth starts, leaf material normally accumulates quite rapidly. Approximately 80% of growth is expected to occur before the end of January. This rapid growth goes hand-in-hand with rapid maturing of the herbage and thus a lower quality of forage is on offer to the animals. Farmers are therefore left with the problem of when, and at what rates, they should stock the veld to ensure that their animals will gain most benefit from it.
A further problem which influences the farmer's management decisions is that sheep concentrate their grazing almost exclusively on short and nutritious forage. If the herbage on offer to them is tall, or if there is a significant carry-over of grass from one year to the next, the sheep will not perform well nor even show mass gains. Typically, if the grasses are allowed to mature and become rank, sheep would avoid these grasses and concentrate on short-growing grasses, or on individual grass tufts and areas of the sward which have previously been grazed short. The regrowth of these previously grazed areas provides forage of a higher quality than the older leaf material. The grazing habit of sheep therefore gives rise to the typical species- and area-selection patterns that can be observed throughout the grassveld where sheep production forms an important component of the farming system.
Where severe species- and area-selection occurs (as is normally the case when sheep are grazed alone or in a high proportion relative to cattle), the palatable species decline in vigour and are usually replaced by species which can tolerate severe defoliation. Soil conditions in these area-selected patches also change due to excessive trampling and the exposure of the soil surface to direct raindrop impact. Such disturbance of the soil and the reduction of vigour of the palatable plants, through severe and regular defoliation, produces conditions suited to a rapid change in species composition. Trampling and increased raindrop impact normally result in compaction of the upper soil layer, thus reducing the rate at which water will infiltrate into the soil. Run-off therefore increases. The lower moisture availability to plants in these patches results in a lower dry matter production potential and the potential grazing capacity of the veld is reduced.
If the process described above is allowed to continue, the veld often degrades to a state where it is dominated by the ‘wire’ grasses (e.g. Elionurus muticus - wire lemongrass) and small, woody karroid shrubs such as Felicia filifolia (aster). Such areas have an extremely low animal production potential. In some sourveld areas, whole hillsides are now in this severely degraded state.
VELD MANAGEMENT FOR SHEEP PRODUCTION IN SOURVELD
Veld management for sheep production systems in the sourveld areas of Natal (and the Eastern Cape and eastern Mpumalanga Highveld) is complex. Most farmers are acutely aware of the grazing habits of sheep, their effect on the veld, and their nutritional needs for satisfactory levels of wool and mutton production. One of the main management options farmers apply in an attempt to address all these requirements is to burn the veld regularly. Fire, in addition to removing old, unpalatable grass which has carried over from the previous season, results in regrowth with a high nutritive value. In fact, the nutritional value of regrowth after a fire is usually higher than regrowth in unburnt swards. Furthermore, after the burn, the grass plants are all generally at the same height (at the same stage of regrowth) and, if the veld is stocked correctly, area selection by the sheep may be reduced.
The veld is often stocked as soon after the burn as possible to ensure maximum benefit to the animals from the high quality of feed on offer to them at this time, and is normally stocked at a relatively high rate to ensure that the grass is kept short. This practice leads to high animal performance and high returns for the farmer. Unfortunately, as the season progresses, the grass ‘gets away’ from the animals, particularly if the sheep are grazing alone. This will happen even if a high stocking rate is applied under continuous grazing as well as in rotational grazing systems. The longer the sheep are kept on the veld during a particular season, the more selective they will become and the pattern of degradation described above will occur.
What options do sheep farmers have to ensure that a profit can be made from the veld and, at the same time, to maintain the production potential of the veld?
First, it is widely recognised that fire is an indispensable tool in the management of sourveld. The vegetation which dominates the sourveld areas is maintained as grassland due to frequent (annual or biennial) defoliation by fire. However, frequent burning, together with frequent intense defoliation through grazing, also results in a lower production potential of the grassland. Approximately 30% of potential spring growth is lost if the veld is burnt after the start of spring. Burning is therefore recommended only every 3rd or 4th year, depending on the growing conditions of the vegetation, and how evenly and completely the veld was grazed during the previous season. Burning should be undertaken while the grass is dormant and at about the time of the first spring rains. Obviously, if the first major ‘spring’ rains are ‘late’, the grass may not be in a dormant state because of earlier light rains. Sourveld should always be burnt before active growth begins (refer to Production Guideline 2.8 of this series for "Burning Guidelines for KwaZulu-Natal" for more detail). It must be stated that if fire is used judiciously the farmer can maintain the veld in good condition and provide nutritious forage for livestock. Animal production can be enhanced through the correct use of fire.
Second, because sheep on their own are not able to graze the veld evenly during the summer and autumn in the year of the burn, and particularly in the second and third years after burning, it is strongly advocated that they should be grazed together with cattle. Cattle are better adapted to graze and use tall mature grass than are sheep. Provided that the correct stocking rates are applied, the introduction of cattle in a grazing system would ensure that the veld is maintained at a short, even height, which provides the sheep with the kind of herbage they prefer to graze and also reduces the need to burn the veld too frequently. A rotational grazing system is also advocated because this tends to promote more even grazing, thus reducing the extent of species- and area-selection, and ultimate veld degradation.
Within any sheep production system, however, some degree of selective grazing is inevitable. Rotational grazing has the advantage over continuous grazing, in that the farmer can manage the system to the advantage of both the animals and the veld. Management actions, such as varying the periods of occupation and absence from camps and providing for prolonged seasonal (e.g. spring, summer or autumn) or year-long rests, allow individual species and areas which have been selectively grazed by the sheep, a chance to recover from such grazing. This promotes the maintenance of the vigour and productivity of the veld. A rotational grazing system also simplifies burning management by allowing individual camps to be burnt while animals are confined to other camps in the system, and it allows for subsequent control by the farmer of post-burn grazing management.
Third, the veld should be stocked correctly. In the drier phases of the sourveld areas of KwaZulu-Natal, veld in good condition has a potential grazing capacity of between 1.6 and 2.2 hectare per AU. Obviously, rainfall and temperatures in any particular season will influence the amount of grass produced and therefore how many AU can be carried during that season. The above figures are given only as a guideline and assume that a good veld management system is being implemented. Two important principles to remember are that a) as stocking rate increases, so individual animal performance decreases, and b) where the stocking rate exceeds the capacity of the veld to produce fodder, veld deterioration is inevitable.
What is the most appropriate cattle to sheep ratio to apply on the farm?. The short answer to this question is that there should be sufficient cattle on the farm to ensure that the camps that the animals are in are evenly grazed. The results of grazing experiments which were conducted during the 1950's and 1960's in the sourveld of the Eastern Cape and the eastern Mpumalanga Highveld, suggested that a ratio of 1 AU cattle (450 kg growing steer) to 1 AU sheep (6 mature sheep), or a ratio which favoured cattle, would be the most favourable for both animal production and for maintaining the veld (Note: an Animal Unit (AU) is defined as a 450 kg growing steer, and this is equivalent to approximately 6 mature sheep). Recent results from a cattle-to-sheep ratio grazing experiment at the Kokstad Agricultural Research Station indicate that these same ratios are also ‘best’ for sheep production systems in the drier phase of the Highland Sourveld of Natal (Table 1).
Table 1. Animal production figures for cattle and sheep stocked at different ratios and at a stocking rate of approximately 1.5 ha per AU. Note that the sheep gains per hectare are given after subtracting wool production.
Ratio (cattle (AU) : sheep (AU)
Mass gains per hectare
(kg)
Body mass
Wool
Cattle
Sheep
1:0
3:1
1:l
1:3
0:1
117
101
72
36
-
-
8.4
6.3
10.0
5.2
-
6.0
11.0
17.0
19.0
Note: The figures are the average of three years of data collection. All three years had an average rainfall of approximately 790 mm which is the norm for the Kokstad Research Station
The experiment was conducted using a rotational grazing system with 3 camps grazed by each group of animals (ratio treatment) in any one season. The results and recommendations after four years of running the trial are summarized below.
- In all grazing seasons, as the proportion of cattle in the species mix increased, sheep performance increased. A decline in sheep performance was recorded in each ratio treatment from the first to the third season. This decline was attributed to the increased maturity and thus lower quality of herbage on offer to the sheep, and the fact that only one paddock available to the animals in the second and third grazing seasons had been burned prior to the start of the season. Sheep performed best during the season which had the lowest rainfall where herbage quality was maintained for longer into the grazing season than in previous seasons.
- In contrast, cattle performance was affected by the stocking rate (animals/ha) of cattle rather than the presence of sheep. As the quantity of herbage on offer per steer declined steer performance declined.
Regarding the impact of grazing on the sward, results of the trial provide strong indications that, in the long-term, the current recommendations of grazing cattle together with sheep in order to prevent the degradation or loss of veld condition which occurs in sheep-only grazing systems, will not succeed. A four-paddock rotation grazing system does not appear to be an appropriate veld management system for sustainable sheep production in sour grassveld. An alternative approach to veld management is suggested in which the sheep are confined to only those areas of the farm which were burnt at the start of the grazing season. Ideally, sheep should not allocated to the same paddock for two consecutive grazing seasons and the paddock which was grazed by sheep should be provided a full season's rest in the following season.
The reader is referred to Production Guidelines 3.3 to 3.6, and 9.8 for detailed discussion on alternative veld management strategies depending on the livestock production system being implemented on the farm.
CONCLUSIONS
- Sourveld in good condition provides grazing for only a portion of the year (8 or 9 months).
- The grazing habit of sheep leads to severe species- and area-selection which result in a deterioration in the production potential of the veld, particularly if sheep are grazed on their own.
- Burning is an essential component of any sourveld management system aimed at sheep production off veld, but fire should not be used too frequently (only every 3 to 4 years).
- Cattle should be grazed together with the sheep at a ratio of 1 AU cattle to 1 AU sheep, or at a ratio in favour of cattle. Cattle remove the taller grass which is not suited to the sheep and thus maintain the sward at an even height. This, together with a good rotational grazing management system, reduces the effects of selective grazing on the sward.
- An appropriate grazing management strategy must be applied for the livestock production system being implemented. The frequency and duration of rest periods, the intensity of grazing and the use of fire will all vary depending on the stocking rate (ha/AU) applied and proportion of cattle and sheep being run on the veld.
- The stocking rate should not exceed the grazing capacity of the veld which, in the drier phases of the sourveld of Natal, ranges between 1.6 and 2.2 ha/AU.