Forage Quality of Ventenata dubia in a Southeastern Oregon Meadow System

Abstract

Ventenata (Ventenata dubia L.) is an exotic annual grass gaining attention for its environmental and economic impacts across the western United States. Since cattle reportedly avoid grazing it, there is speculation regarding why it is rejected, though little is known about its forage quality and digestibility. We examined the seasonal and annual forage dynamics of ventenata in a southeastern Oregon meadow system by analyzing the forage quality (crude protein, acid detergent fiber, lignin); silica content; in vitro digestibility (IVDMD); and macrominerals (phosphorous, calcium, magnesium, potassium, and sulfur) of ventenata over the growing season (May, June, and July) for 2 yr. We did not find that ventenata is low in forage quality, macrominerals, or digestibility. Overall, the forage quality of ventenata, especially in early spring (May and June), appears to pose little issue nutritionally. In fact, the crude protein of ventenata stayed above the crude protein minimum requirement for maintenance in grazing cattle through June. However, we did find that silica content as acid insoluble ash content (AIA%) of ventenata at our sites increased throughout the growing season and ranged between 4.3% and 12.1%, nearly 4× the amount previously reported. We also found variability in digestibility and nutrient profile from year to year that can be related to annual precipitation. For example, digestibility decreased by June in the wetter year but did not decrease in the dryer year until into July. Our results have implications for the management of ventenata and are especially relevant for the consideration of targeted grazing as a control method. Forage quality and digestibility of ventenata are best in early spring but, due to the height of the annual grass during this time, there is only a brief window for a targeted grazing strategy because its quality and digestibility declines and silica content increases over the growing season.