干旱区生态环境知识资源中心

The influence of stocking rate on vegetation and animal performance was investigated over a period of 15 years in the Semi-arid Sweet Bushveld of Southern Botswana. The objective of the study was to establish an appropriate stocking rate for the area and evaluate the relationship between animal performance and the available herbage. The trial compared steers grazing at 2, 4, 6, 8, 10 and 12 ha per livestock unit and a non-grazing area. Herbage yield, steer live mass gain and carcass price were the responses measured. Herbage yield was collected from randomly clipped quadrats at the end each growing season. Grass species were grouped according to nutritive value as good, intermediate and poor. The trial was restocked each year with 18-months steers. Steer were weighed at monthly intervals and were slaughtered at the end of the grazing year where carcasses were graded and given a price. Forage yield of good and poor grasses increased and decreased, respectively with decreasing stocking rate. The yield of intermediate grasses increased at heavy grazing and declined at lower stocking rates due to competition from more productive perennial grasses. Live mass gain of individual steers increased with decreasing in stocking rates. Steers at 8 ha lsu(-1) gained almost similar to those in 10 and 12 ha lsu(-1) at the expense of the good grasses suggesting that range deterioration may progress for a considerable time before the change is reflected in animal condition. Therefore herbage condition is more sensitive indicator of range deterioration than the condition of the grazing animals. Mean annual livemass gain of approximately 100 kg or more can be achieved on Semi-arid Bushveld with only phosphorus supplementary feeding at 8 ha lsu(-1) or lower stocking rates. Annual livemass gains for individual steers varied considerably from year to year suggesting flexible stocking rates between 8 - 10 ha lsu(-1) could be applied depending on rainfall amount. Optimum stocking rate on the basis of good grass species is 10 ha lsu(-1) for the Semi-arid Sweet bushveld.