The Effects of Livestock Grazing on Forb Quality and Quantity: Implications for Pronghorn Habitat Management

Jacob C. Locke, Carlos E. Gonzalez, Justin T. French, Louis A. Harveson, and Shawn S. Gray (TPWD)

Pronghorn (Antilocapra americana) and cattle cohabitate on many North American grasslands. While livestock grazing is known to influence the vegetation composition of a rangeland, the effects different livestock grazing systems have on forb communities for pronghorn are not well understood.

We sampled forbs at the peak of growing season in September 2018 and 2019 to assess the effects of rotational and continuous cattle grazing regimes on forb quality and production. We hypothesized rotational grazing would increase the nutritional quality of the forb community and overall forb production, compared to continuous grazing and no grazing. We randomly sampled pastures subject to continuous and rotational grazing, as well as grazing exclosures using 96 (rotational grazing), 100 (continuous grazing), and 64 (no grazing) plots. We compared the quality of available forbs and total forb production among grazing regimes using redundancy analysis.

We found that the effects of grazing varied by year. In wetter conditions, rotational grazing exhibited higher forb quality and biomass, while exclosures exhibited such results under dryer conditions. The knowledge gained from this study helps wildlife biologists and landowners understand how cattle grazing affects the quality and production of available forbs, which are critical components of pronghorn habitat quality. Our results suggest that rotational grazing offers benefits to managers seeking to promote pronghorn forage quality, when rainfall is adequate. We also suggest that managers adjust grazing intensity, or even defer grazing, under dry conditions to similarly promote forb quality and production.

Funding sources: Texas Parks and Wildlife Department, Texas Parks and Wildlife Foundation, and San Antonio Livestock Expo.