The University of Arizona

Evaluating grazing strategies for cattle: deer forage dynamics.

I.M. Ortega, S. Soltero-Gardea, F.C. Bryant, D.L. Drawe


We documented vegetation dynamics (April 1986-July 1989) as part of a larger study to understand botanical composition and nutritional components of cattle and deer diets under 2 grazing systems (continuous and short-duration), and 2 stocking rates (heavy and moderate) at the Welder Wildlife Refuge, Sinton, Tex. Objectives of the study were to examine initial vegetation homogeneity and floral changes over time in the plant community, and to determine phytomass dynamics. Results indicated that grazing treatment had no impact on homogeneity of the plant community. Cattle grazing, regardless of treatment, increased diversity with time until drought conditions persisted and diversity declined. Shannon's diversity index (H) changed from a pretreatment value of H=2.41 in April 1986, to H=3.08 in April 1988, to H= 2.61 in April 1989. There was no difference (P>0.05) in diversity index between grazing treatments or replication within years. Stocking rates (heavy = 198 g/m2 differed (p< 0.05) from moderate = 258 g/m2) had a more significant impact on phytomass than grazing system (continuous = 225 g/m2; short-duration grazing = 231 g/m2; P > 0.05) by the end of the study period. Precipitation was a determinant factor in the seasonal dynamics of phytomass of the various forage classes. Phytomass of forbs was unaffected by grazing system or stocking rate. Phytomass of grasses and grass-like plants important to deer was lower (P < 0.05) under short-duration than continuous grazing. Phytomass of grasses and grass-like plants preferred by deer was greater under moderate than heavy stocking rate. We recommend continuous over short-duration grazing, and moderate over heavy stocking rates, when whitetailed deer habitat quality is a primary concern. Less intensive grazing systems should be acceptable as well.


continuous grazing;rain;Odocoileus virginianus;stocking rate;forbs;rotational grazing;grazing intensity;cattle;Texas;biomass;seasonal variation;botanical composition;grasses;feeding preferences

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