The Carrying Capacity of Pastures

Abstract

The data from all published results of grazing trials in which three or more rates of stocking were compared for one or more years were examined. Where possible regression equations and correlation coefficients were calculated. In many cases, a significant negative correlation was found between stocking rate per acre and liveweight gain per animal per day. In no case was the relationship positive, and no point of discontinuity was found in the linear relationship. The slope of the line appeared to be related to the length of the grazing season; the longer the season, the steeper the slope. The application of these results in practice is discussed in agronomic and economic terms.The carrying capacity of a pasture or range is the number of animals of a specified type that can subsist on a unit area and produce at a required rate over a specified period, usually a season, a year, or longer.To achieve maximum output it is important that the carrying capacity of pastures should be known. This is not an easy thing to measure because of difficulties in measuring the quantity of available nutrients per unit of land. It is not an easy thing to achieve, even then, because of difficulties in utilizing what is available. These difficulties stem from an imbalance in the herbage of nutrients required by the animals and from poor sward structures from which animals are unable to obtain enough food.An optimum stocking rate is that which allows grazing animals to produce at the most economic rate. This rate may not be the maximum possible, as it depends on the economic relationship between the value of the pasture and the product, and the costs associated with the necessary grazing management. As the costs and values of these input and output factors vary from time to time and from place to place according to the laws of supply and demand, it would be of great assistance to producers of animal products to know approximately how production per animal and per acre is affected by the stocking rate per acre per grazing period.On all but annual pastures the effect of any previous grazing will be seen in the current productivity of the pasture and trials must be continued for several years in order to measure any efFects on animal production of pasture degradation due to overgrazing or understocking. Stocking rate has an effect on the quantity of herbage grown, the proportion eaten and the amount eaten by each animal. It has been shown by Mott (18) Riewe (20) and Cowlishaw (8) that the relationship between stocking rate and liveweight gain per acre is curvilinear. Riewe (20) and Cowlishaw (8) showed from their data that the relationship between stocking rate and liveweight gain per animal appeared to be linear. Harlan (10) suggested the use of a double exponential equation, but he calculated stocking rate ia terms of acres per animal. Using the reciprocal of this term (animals per acre) for his data also produces a straight line relationship (Riewe, 21).Petersen, Lucas and Mott (19) produced some equations based on a number of assumpti...

Change of Composition and Diversity of Species and Grassland Management Between Different Grazing Intensity in Pannonian Dry and Wet Grasslands

“…Over-grazing, as a concept -in terms of grassland management -indicates the grazing animal carrying capacity, the maximum number of tenable species/varieties per area unit, and the number of livestock kept for a period in order to produce needed product. An optimum stocking rate is the value, which regulate the number of grazing animals at the most economical rate (Cowlishaw, 1969). Over-grazing can be interpreted as an indicator of the actual number of livestock, but its time/interval defining dimension/role is more important (Pratt, 2002).…”

Stocking rate trials in Ankole, Uganda: I. Weight gain of Ankole steers at intermediate and heavy stocking rates under different managements

“…In 3 out of the 4 years the weight gain/animal was higher from treatment 0-6C than the expected straight line relationship between these two variables would have predicted (Riewe, 1961;Cowlishaw, 1969). 1970 gave an anomalous result for treatment 0-6C (see above).…”

“…Cowlishaw (1969) reviewed 22 trials, on a wide variety of pastures, and none revealed any discontinuities from a straight line relationship, except under very high grazing pressures, when the weight gain was sometimes lower than expected. In the current trial the highest stocking rate gave a higher gain than expected.…”

Integrated Modeling of Land and Water Resources in two African Catchments

“…We used the concept of carrying capacity (Cowlishaw, 1969) to characterize the sustainability of grazing. Carrying capacity, with respect to livestock grazing, refers to the number of grazing animals a landscape is able to support without depleting rangeland 102 vegetation or soil resources.…”