Swath Grazing: Extending The Grazing Season

By Sandy Smart
Professor & SDSU Extension Rangeland Management Specialist

Producers are always looking to cut costs in livestock operations because of marginal profit opportunities in commodity based markets. One proposed way to cut fall/winter feeding costs is to extend the grazing season and allow the livestock to harvest the resource instead of relying on mechanical harvest. This will reduce the labor required to cut, bale, and feed hay. At issue is the harvest efficiency of grazing versus mechanical harvest and the costs associated with each enterprise. Grazing is an inefficient process (see Figure 1), especially during the growing season when residual leaf material is needed to maintain plant vigor. In extensive grassland systems this efficiency is usually 25% and under more intensive management it could approach 35% under moderate grazing pressure (25 AUD·Mg-1).

However, after a plant sets seed or after a killing frost, less residual leaf material is needed to ensure plant vigor and therefore a greater grazing pressure can be applied to increase the harvest efficiency. In this situation, we might increase harvest efficiency to 50% under very heavy stocking rates or grazing pressures that approach 50 AUD·Mg-1 (Figure 1). By contrast, haying could be as high as 80 to 90% efficient depending on the cutting height. Combining the advantages of these two techniques (high harvest efficiency of cutting and low labor costs of grazing) is the underlying principle behind swath grazing.

Figure 1. Forage disappearance as affected by grazing pressure (animal unit days per 1000 kg of forage; AUD·Mg-1) Source: Smart unpublished data.

Determining Swath Grazing Efficiency

Harvest efficiency of swath grazing can be calculated by multiplying the efficiency at harvest time by the efficiency of grazing the swaths in the fall and winter. Typically we might assume 80% harvest efficiency at cutting and a 75% efficiency during the grazing of the swaths. Therefore we would realize a 60% overall harvest efficiency (80% x 75%). In order to increase the grazing efficiency, strip grazing the swaths can help to lessen the wastage (Figure 2 and Figure 3).

In this operation, the producer spends about ½ hour per day to move the temporary electric fence to allocate the new swaths. Feeding hay using round bales would take a similar amount of time but would also include the costs of running the tractor. Therefore, the producer is eliminating the costs associated with baling and bale moving portions of the haying enterprise.

Figure 2. Cattle grazing swathed intermediate wheatgrass in January at the Wagner Ranch near Chamberlain, SD. Ungrazed swaths are on the right and grazed swaths are on the left. Photo by T. Gompert.