agricultural production guidelines
m
Veld in KwaZulu-Natal
Co-ordinated Extension KwaZulu-Natal Veld 8.2 1999
STOCKING RATE
J R Turner
P O Box 10, Babanango 3850
Factors
Influencing Stocking Rates
Effect of Stocking Rate
on Veld Condition
Effect of Stocking
Rate on Animal Performance
INTRODUCTION
Stocking rate refers to the area of land allocated to each animal unit in a grazing system, and, in the case of veld, is usually expressed as the number of hectares per animal unit (ha/AU). Whether a farm is overstocked, correctly stocked or understocked depends on the grazing capacity of the veld. Grazing capacity is a function of the veld, while stocking rate is manager dependent. The stocking rate that is applied is usually the farmer's estimate of the grazing capacity (Danckwerts, 1985). Stocking rate is therefore one of the most fundamental variables under the control of the manager.
Stocking rate is one of the most important factors affecting individual animal performance and veld condition. It exerts a major influence on the income, and therefore also the profitability, of the livestock enterprise. The objective on stock farms is usually to maximise profit within the constraints of veld stability. This implies acceptable animal performance in the short-term, and the maintenance or improvement of veld condition for sustaining acceptable levels of animal performance in the long term.
Stocking rate can be adjusted relatively simply, either by decreasing or increasing stock numbers. These adjustments are not always easy to apply seasonally to account for short-term fluctuations in the grazing capacity of the farm. Adjustments can, however, be implemented to cater for longer-term fluctuations in grazing capacity. Adjustments to stocking rate are more easily implemented if the herd structure lends flexibility to allow for them.
The objectives of this Production Guideline are:
- the important factors influencing the production potential of the veld and therefore the stocking rate that can be applied;
- the effect of stocking rate on veld condition; and
- the effect of stocking rate on animal performance.
FACTORS INFLUENCING STOCKING RATES
The two overriding factors which influence veld stocking rate are climate and the condition of the veld.
The two climatic factors which have a major influence on grass production, and therefore the stocking rate which can be applied to veld, are rainfall and temperature. Moisture is the factor most generally limiting grass growth. In the Valley Bushveld and Lowveld (Bioresource Groups 21 and 22) rainfall has an almost overruling influence on grass growth. Rainfall in these areas is very unreliable and erratic. In other similarly dry regions of South Africa, three-fold and greater differences in grass production have been demonstrated at the same site over different seasons due to variation in rainfall.Climate
In the Highland Sourveld (Bioresource Groups 8 and 9) the influence of temperature is most important. This applies particularly in spring, where temperature and not moisture is often the main factor affecting grass growth. Rainfall in these areas is also more reliable and less erratic.
In the Moist and Dry Tall Grassveld and the Sour Sandveld (Bioresource Groups 11 to 16), both rainfall and temperature will affect grass growth, although rainfall will be relatively more important. Rainfall in these areas is also erratic. Fluctuations in rainfall have the greatest influence on seasonal variation in grass growth at a particular site. Planning for these fluctuations, parti-cularly the setting of stocking rates, is therefore extremely important.
Veld condition
Veld condition has a marked influence both on the amount and the quality of the forage produced, and therefore on the rate at which the veld can be stocked. In the mixed veld and sweetveld areas of KwaZulu-Natal, forage production from veld considered to be in good condition is far greater (about double the available forage) than from that considered to be in poor condition. In the Sour Sandveld (sourveld) the quantity of unacceptable material is far greater in veld considered to be in poor condition than in veld considered to be in good condition (Turner, 1988).Veld in good condition should therefore have species which have both a high production potential and which are acceptable to the grazing animal. In KwaZulu-Natal, veld regarded to be in good condition is usually dominated by redgrass (Themeda triandra), but there are several other important grazing grasses which vary in different areas. For example, in the Lowveld, Guinea grass (Panicum maximum) is important, while in the Tall Grassveld, tridentgrass (Tristachya leucothrix) and common thatchgrass (Hyparrhenia hirta) are important at various times during the season.
EFFECT OF STOCKING RATE ON VELD CONDITION
The more heavily veld is stocked, the more intense will the sward be defoliated. Frequent and severe defoliation results in reduced plant vigour and therefore a decline in veld condition. The pattern of veld degradation resulting from heavy stocking rates in sourveld is different to that in sweetveld.
Veld degradation in the sourveld generally occurs through the replacement of the desirable species such as redgrass, by less desirable species such as ratstail dropseed (Sporobolus africanus) and fan lovegrass (Eragrostis plana). A reduction in cover is therefore not generally seen. Because these species still have a relatively high production, total grass production per se is not necessarily affected to any marked extent. The quality of the herbage produced, however, has a lower nutritional value and a lower acceptability to the animal. Sourveld has a high stability and therefore changes due to management are relatively slow. However, it is not resilient, in that, once the changes have occurred, it is difficult to revert the veld back to its original composition.Sourveld
Sweetveld
The pattern of veld degradation which is usually
observed in sweetveld is firstly the disappearance of the desirable species such
as redgrass and Guinea grass, resulting in a reduction in cover, followed by the
establishment of less productive grasses such as bushveld signalgrass (Urochloa
mossambicensis), bushveld dropseed and pan dropseed (Sporobolus ioclados)
on the relatively sparsely-covered ground. The effect of degradation is
therefore largely a reduction in dry matter production rather than a reduction
in quality. In savanna areas, this degradation is usually accompanied by an
increase in bush density. Sweetveld has low stability because changes due to
management are relatively fast. It is, however, resilient, in that, if managed
correctly, it can revert relatively quickly to a situation similar to that which
existed before the changes occurred, provided that soil losses were not
excessive.
In both sourveld and sweetveld, the adverse effect of stocking rate on veld condition will cause the farmer to suffer a long-term loss in animal production, and the future economic stability of the enterprise will be affected. Farmers therefore cannot afford to overstock.
EFFECT OF STOCKING RATE ON ANIMAL PERFORMANCE
The general effect of stocking rate on animal performance from sweetveld and sourveld is illustrated in Figure 1. At light stocking rates, gain per animal remains constant in sweetveld where animal potential, and not the quality of the forage, is the factor limiting animal performance. On the other hand, gain per animal may increase in sourveld and mixed veld where the quality of grass, and not the potential of the animal, is the factor limiting animal performance. At heavier stocking rates, gain per animal decreases as stocking rate increases.
Figure 1. Illustrative relationships between stocking rate and gain per head on sweetveld (A), gain per head on sourveld (A'), gain per ha (B), and profit per ha (C).
The effect of the relationship between gain per head and stocking rate, on gain per ha and profit, is presented in Figure 1. Initially, gain per ha increases as stocking rate increases (initially the increase in the number of animals more than compensates for the decrease in gain per head), and then declines (after point Bmax the increase in number of animals no longer compensates for the decrease in gain per head).
The economic optimum stocking rate is seldom as high as that at which maximum gain per hectare is achieved, and, in practice, it usually occurs somewhere between the stocking rates at which maximum gain per head and maximum gain per hectare are achieved (Figure 1). In beef production, it is usually closer to the stocking rate at which maximum gain per head is achieved because a decrease in animal performance is usually also accompanied by a decline in price, due to the poorer grades obtained (Gammon, 1986).
Economic analysis of stocking rate trials reveals that the economic optimum stocking rate will usually occur at a point at which gain per head is more than 90% of the maximum (Gammon, 1986). In practice, it is difficult to establish the economic optimum stocking rate or the stocking rate above which veld deterioration begins, but a good, and conservative, approximation can be achieved by adjusting the stocking rate to produce animal performance close to the maximum performance per head (Gammon, 1986; Turner, 1988; Danckwerts, personal communication). Gammon (1986) also suggested that in sensitive veld types, point B is often associated with a stocking rate at which veld deterioration occurs (which is not in keeping with the objective of sustained production). For example, heavy utilisation of the veld occurred at such a point in the Sour Sandveld (Turner, 1988). It was also suggested byTurner (1988) that veld utilisation at stocking rates where gain per head was at, or close to, a maximum, should be sufficiently lenient so as not to adverselyaffect veld condition. Both the economic and biological incentives for stocking close to the point at which maximum performance per head occurs, are high.
LITERATURE CITED
DANCKWERTS, J.E. 1985. Overstocking can lead to insolvency. Golden Fleece, May 1985.
GAMMON, D.M. 1986. The importance of stocking rate in veld management and animal production. Cedara : Department of Agriculture & Water Supply.
TURNER, J.R. 1988. Towards the development of a grazing capacity model for the drier grazing areas of Natal. M.Sc.Agric. Thesis, University of Natal, Pietermaritzburg.