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Spring Cattle Grazing Reduces Nutrients Available to Mule Deer

PULLMAN, Wash. — Recently released results from the nutrition component of the Pilot Grazing Project conducted in 2009 in southeast Washington reveal that moderate spring cattle grazing affected both the amount and some nutritional properties of forages available to mule deer in spring and fall.

Drs. Lisa Shipley and Linda Hardesty and their students at Washington State University are conducting the project, a joint effort of Washington Department of Fish and Wildlife and the Washington Cattlemen’s Association. Research has shown that cattle grazing can be effective at reducing old grass and promoting younger, more nutritious forage for wildlife. The Pilot Grazing Project evaluates this premise on the bluebunch wheatgrass grasslands of the Chief Joseph Wildlife Management Area.

Limited spring grazing is the most common cattle grazing strategy on these types of grasslands. Graduate student Sara Wagoner collected forage samples in spring and fall from paired grazed and ungrazed plots located in three pastures that cattle grazed in spring 2009. The study was conducted on the area’s driest, least productive vegetation type, thus defining cattle grazing’s most extreme possible impact. Mule deer diets on grazed and ungrazed plots were determined by grazing tame mule deer in the plots and collecting comparable diet samples for analysis.

Deer on the grazed and ungrazed plots consumed diets of equal digestibility and energy, but the grazed plots provided higher protein diets on two of the three pastures. However, the deer consumed more total forage and energy on the ungrazed plots. When combined with reductions of 40–50 percent in available forage, the number of deer an acre of forage could support for a year was lower on the grazed plots. Wild deer and elk grazed the plots between the spring and fall sampling and probably accounted for some reduction in available forage. It is not clear if the effects of cattle grazing continue beyond the grazing year. However, these results do not support the idea that spring cattle grazing will produce more nutritious forage for mule deer on these grasslands.

The pastures’ ecological integrity is also being investigated over a four-year period. The results of this work, available in 2012, will evaluate any longer-term impacts of cattle grazing on soils or vegetation.