Stocking rate
The stocking rate indicates the number of livestock that are carried per unit area for a specified period. To meet the requirements for efficient management, the stocking rate usually coincides with the grazing capacity or production potential of the vegetation. The difference between the terms stocking rate and grazing capacity is that grazing capacity describes the production potential of the vegetation while stocking rate indicates what numbers of stock are run after the manager has estimated what the grazing capacity is, or what land-to-animal relationship (stocking rate) will provide the most beneficial returns. Where the stocking rate is higher than the grazing capacity, the term over-stocked is used while the term under-stocked is used to indicate that the stocking rate is lower than the grazing capacity of the veld.
Stocking pressure
Stocking pressure describes the mass of available forage per specified animal unit at any instant of time. Since the availability of forage is dependent on several factors, including the appetite of the animal, criteria for estimating forage availability should always be stated.
Stocking density
Stocking density is the ratio between the number of specified animal units and the land area (ha) at any instant in time and is expressed as animal units/ha. The stocking density is dependent on the grazing system. In a continuously grazed system, the density of stock at any instant of time is reflected by the stocking rate. However, in a rotational system, this is not so and the actual density of stock is dependent on the system.
Period of occupation, period of stay and grazing period
The stocking density provides a measure of the degree of concentration of animals but does not provide information on the management aspect of how long the animals are concentrated on an area of land. The period of occupation is the length of time for which a particular area of grazing is occupied without interruption. On the other hand, the period of stay is the length of time for which a particular group of animals grazes without interruption. Thus, for example, if one group of animals follows another group in the rotation the period of occupation is the sum of the two periods of stay.
For a fuller understanding of grazing capacity and stocking rate, it is necessary to define the grazing period. The grazing period is the period during the year for which a particular pasture will normally provide acceptable grazing for livestock: the calendar months should be specified, e.g. 180 days – October to March.
Stocking intensity
Stocking intensity is a single term describing two important aspects of management: (i) stocking density and (ii) period of occupation. Booysen (1967) defines stocking intensity as a mathematical expression reflecting simultaneously both the degree of concentration of animals and the length of a grazing spell and is derived by dividing the stocking density (expressed as AU/ha) by the period of occupation (expressed in days).
Period of absence and period of rest
Closely related to the period of occupation in a rotational grazing system is the interval between successive periods of occupation.
The period of absence from a camp in a rotational grazing system is the length of time between successive periods of occupation during which the sward regrows to a stage suitable for grazing. The period of absence from a camp is not one of rest for the grassveld itself, but to provide time for the accumulation of adequate regrowth for the animals at the next grazing.
The period of rest, on the other hand, is defined by Booysen (1967) as the length of time during the growing season when a paddock is offered uninterrupted rest from grazing to restore the productivity of the sward by any of the following means, such as allowing of seeding or root growth, or replenishment of root reserves.
Grazing cycle
A single rotation through the camps of a system constitutes a grazing cycle. The duration of the cycle may be constant or may, in a flexible system, vary at the whim of the manager or due to variation in pasture growth rate.