How can ranchers improve profitability when feed typically represents well over half of cow-calf production costs? Grazing dormant winter range is a common practice to reduce costs in South Dakota. Grazing winter range when plants are completely dormant minimizes negative impacts on the function of the plant during the growing season. Separate pastures are typically designated for winter use only, often based on availability of winter shelter, water and access to stored feeds.
In practice, winter pastures are often deferred from grazing during the growing season to allow for grass to stockpile for winter grazing. Is deferred grazing the best option for maximum production? Initial response would be yes. However, research has shown that carefully planned defoliation or grazing during the growing season may stimulate plant production. Therefore, designing a system that allows for some grazing when plants are growing (i.e. spring) could possibly increase the use of winter pastures without sacrificing the amount of stockpiled forage.
In western South Dakota vegetation is dominated by cool-season grasses, so that a majority of plant growth occurs in April, May and June which corresponds with peak moisture months. Expectations would be that plants reach maximum height and yield about by July 15. Based on this knowledge, we would anticipate plants grazed after July 15 would not have sufficient regrowth potential to accumulate for winter grazing.
This brings us to the question when is the right time to graze? Research was conducted at SDSU Cottonwood and Antelope Research Stations in western South Dakota for three seasons to test the hypothesis that clipping early in the growing season at a low intensity would allow adequate regrowth, compared to winter clipping only. Treatments included either a 25 or 50% relative utilization of the current stand of western wheatgrass. Clipping dates were May 15, June 15, July 15 and August 15. An additional treatment was no clipping during the spring or summer. Using previously established height/weight relationships, production was estimated by measuring the plant height of western wheatgrass. Quantities of short and mid grasses were determined at the conclusion of the study to see if there was any shift in plant community composition.
Results of the study suggest that grazing winter pastures in May, targeting 25% relative utilization, allows sufficient regrowth to occur during the remainder of the growing season to maintain sufficient stockpiled forages for winter use. Human nature is to push the limit by either increasing utilization or extending the grazing period. Based on the results, we need to be cautious not to graze at a higher utilization rate in May (50%) or extend the grazing period into June even at a lower utilization rate (25%). Standing forage available for winter use could be reduced. There was also a negative shift from mid to short grasses when plots were clipped in June. Results are consistent with other research demonstrating that grasses are most vulnerable during the rapid elongation phase of growth. Timing of this event may vary considerably from one year to the next. Excellent grazing management requires adapting grazing schedules in response to growing conditions and plant development.