Resource Utilization

Grazing indigenous grasslands is considered one of the most sustainable of all agricultural production systems.[1] Dependence of extensive beef production on the underlying natural resource base necessitates that the first level of management addresses that foundation. Establishing a constant or increasing long-term trend in carrying capacity is seen as essential to economic sustainability of the production system. This is accomplished by blending ecological, economic, and animal management principles.[2] Attention to stocking rate, grazing systems, class of cattle, and season of use provide management with critical control points to individually and collectively affect this trend.

Stocking rate is the primary determinant affecting the relative success of any grazing management strategy.[3] This is because stocking rate determines the amount of forage available per animal. On a short-term basis, increasing stocking rate above a site-specific threshold results in forage intake per animal that is less than optimal, and thus individual animal performance declines (Fig. 1). Moreover, because grazing animals such as beef cattle are selective grazers (i.e., they prefer certain plants and plant parts over others), the frequency and severity of defoliation vary among individual plants. Thus, as stocking rate is increased, competitive relationships among plant species are altered, potentially causing changes in plant species composition that favor undesirable plant species over desirable species. The resulting long-term effect is a further decline in animal performance.

The effect of stocking rate on production per unit area of land is a direct function of individual animal performance and stocking density. Thus, production per unit area increases as stocking rate increases, up to some maximum beyond which it rapidly declines (Fig. 1).

The fundamental relationships are further complicated by variation over time and space in the amount of forage available for animal consumption. Therefore, the optimal stocking rate for maximizing production per unit area varies broadly over time and space and only becomes apparent in retrospect. In extensive beef production systems, the management challenge to optimize production in a highly variable (i.e., high risk) environment is truly formidable.

Grazing systems serve to alter the distribution of grazing intensities over time and space. Reducing grazing pressure on plants when they are vegetative allows them greater opportunity to accumulate energy reserves and thus increase their vitality. Conversely, increasing grazing pressure on plants when they are vegetative affords them less opportunity to accumulate energy reserves and thus decreases their vitality. However, the nutritional value of perennial plants is greatest while they are vegetative. Hence, a grazing system must manage the tradeoff to achieve its maximum long-term benefit. A practical and effective grazing system is characterized by six princi-ples:[2] 1) It satisfies physiological requirements and is suited to life histories of primary forage species; 2) it improves the vigor of desirable species that are low in vigor or maintains desirable species in more vigorous condition; 3) it is adapted to existing soil conditions; 4) it will promote high forage productivity; 5) it is not overly detrimental to animal performance; and 6) it is consistent with operational constraints and managerial capabilities.

Stocking Rate

Fig. 1 A conceptual model showing relationships between stocking rate and livestock production. The upper panel illustrates production per animal and the lower panel illustrates production per unit land area. In each panel, the upper curve indicates the functional relationship during periods of high forage productivity relative to periods of more limited productivity illustrated by the lower curve. Vertical dashed lines indicate the relationship between maximum production per unit area (lower panel) and production per animal (upper panel).

Stocking Rate

Fig. 1 A conceptual model showing relationships between stocking rate and livestock production. The upper panel illustrates production per animal and the lower panel illustrates production per unit land area. In each panel, the upper curve indicates the functional relationship during periods of high forage productivity relative to periods of more limited productivity illustrated by the lower curve. Vertical dashed lines indicate the relationship between maximum production per unit area (lower panel) and production per animal (upper panel).

Fencing the resource into pastures facilitates grazing management in many production systems. However, the capital investment in fencing should be evaluated relative to financial returns from the use of an appropriate grazing system. Alternative management interventions may achieve some goals usually attributed to grazing systems. For example, developing additional watering points, strategic placement of salt, and herding can also be used to alter the distribution of grazing pressure and may be more economically viable tactics in extensive beef production systems. Shifts in the time of calving and weaning can also affect grazing pressure, in response to changes in the energy requirements of lactating versus nonlactating cows.[4]

Grazing multiple classes of cattle may offer significant advantages to beef producers. For example, a cow calf enterprise of a magnitude that can be maintained by the natural resource base in all but the least productive years and a stocker enterprise that uses surplus forage when it is available may be a more efficient production system than either enterprise separately.

can return economic benefits to cow calf producers upwards of $70 per cow per year.[5,6] In low feed resource situations, such as characterize extensive beef production, heterosis and the risk associated with improperly matching the biological type of cow with the environment tend to be greater than with more abundant feed resources. Thus, crossbreeding is an important technology for extensive beef production. Like all technologies, successful implementation of a crossbreeding system depends on management. Crossbreeding systems that use sires of two or more breeds may increase variability in the calves to be marketed. Some crossbreeding systems also require multiple breeding pastures and the identification of cows by their year of birth and/or the breed of their sire.

It is important to match the biological type of cow to the environment in which she is to produce.[7] In an environment characterized by high annual precipitation, abundant high-quality forage during the grazing season, and plentiful winter feed, the proper biological type would be a high-milking and fast-growing cow with an early age at puberty. However, if the environment is more limiting, as would be typical of most extensive beef production systems, then the proper biological type of cow would have reduced potential for both milk production and growth, but would retain the ability to reach puberty at an early age. Figure 2 can be used as a way of visualizing this matching process. Being conservative in the matching process wastes feed resources and forgoes income. Over matching the environment by using cows that require too much energy for maintenance and production increases

Fig. 2 Matching maternal biological type (as characterized by weight and milk production) to the forage environment (as determined by precipitation). Values within the shaded areas of the figure reflect increments of annual precipitation and/or represent availability of feed resources.

BREEDING SYSTEMS

Heterosis, which is of greater magnitude in harsh environments than in environments that are more favorable,

Fig. 2 Matching maternal biological type (as characterized by weight and milk production) to the forage environment (as determined by precipitation). Values within the shaded areas of the figure reflect increments of annual precipitation and/or represent availability of feed resources.

sensitivity of output to the naturally occurring variation in feed resources.

Using terminal sire breeds allows producers in extensive production situations the opportunity to match maternal genetic resources with the environment, and simultaneously to match composition of the beef produced with consumer expectations. Crossbreeding systems that employ a terminal sire breed also provide greater flexibility for rapid adaptation to changing markets.

0 0

Post a comment