Saturday, April 19, 2014

Managing Drought Risk on the Ranch

Grazing Pressure & Stocking Rate

The likelihood of overgrazing preferred plant species increases as grazing pressure increases. 

Grazing pressure is the demand/supply ratio between dry matter requirements of livestock and the quantity of forage available in a pasture at a specific time.

Reducing the length of the summer-grazing season and increasing herd size to obtain the same end-of-season stocking rate increases grazing pressure regardless of grazing system.

Stocking rate is the number of animal units per acre for a specified amount of time. Several years of stocking rate, animal performance, and precipitation records can be used to identify levels of stocking beyond which undesirable plant or animal responses begin to occur.

Stocking rates are generally expressed as units of forage demand per unit of real estate. Livestock don’t consume real estate. They consume plants. Stocking rates must be reduced when drought is likely to extend into the rapid-growth windows of dominant forage and browse species.

Carrying Capacity

Maintaining the ecological integrity and financial solvency of ranches requires an understanding of carrying capacity. There are biological limits for animal numbers on every ranch.

Carrying capacity is foremost a timing and a level of forage demand that does not reduce vigor of preferred plant species or the hydrological condition in consecutive years. Conversely, it is also a level of stocking that allows livestock to achieve target levels of production and reproductive efficiency.

The proper number of animals depends on livestock weight and nutrient requirements, and the length of the grazing season. Real estate land values do not alter the biological constraints of carrying capacity.

Consider a Moderate Stocking Rate

Higher stocking rates increase cumulative grazing pressure and increase the risk of damage to vegetation.

Animal performance is less certain with high stocking rates, especially with variable precipitation. Inadequate plant cover increases runoff losses of precipitation and reduces soil water content. Therefore, maximizing yield of animal product per acre requires relatively high levels of ecological and economic risk.

Moderate stocking rates reduce ecological risks by leaving more herbage for ecosystem functions and increase the likelihood of optimizing net return per animal sold off grass.

Stocking Rate Must Consider Current Animal Size

Determining the appropriate herd size to achieve proper stocking depends on kind, class, and weight of grazing animals. Livestock forage requirements can change measurably with changes in weight and/or reproductive status.

The average weight of livestock on many ranches has changed over time. Increases in average mature cow weights and calf weights caused by genetics and earlier calving dates increases animal-unit equivalents per cow-calf pair by 30% to 50%. Without reduction in herd size, these changes increase stocking rate by 30% to 50%.

Determine Stocking Rate and Sustainable Stocking Rate

Grazing records

If grazing records are not available, now is the time to begin. Record the class and number of livestock, and all dates of entry and removal for all livestock for each pasture. Animal unit equivalents (AUE) can be estimated by dividing average animal weights for the grazing season by 1,000 lb. Add average offspring weight to dam weights when the average age of the offspring is 3 months. Grazing records are essential for making intelligent changes in grazing management plans.

Tools

Printable grazing record forms, instructions, and examples from UNL Extension(click on "PDF" to access documents)

Stocking Rate, Forage Inventory, Livestock Inventory Tools (look at Section 3. This chapter is part of the NRCS National Range and Pasture Handbook)

Resources

Integrating Management Objectives and Grazing Strategies on Semi-arid Rangeland

Using Forage Harvest Efficiency to Determine Stocking Rate (TX A&M)

The National Drought Mitigation Center | 3310 Holdrege Street | P.O. Box 830988 | Lincoln, NE 68583–0988
phone: (402) 472–6707 | fax: (402) 472–2946 | Email Us

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