Influence of Temperature and Precipitation on the Forage Quality of Bluebunch Wheatgrass and Idaho Fescue During the Dormant Season

Dormant forage is generally understood to be low-quality, but how and why it changes over the dormant season have not been well studied. Therefore, this study evaluated the changes in the forage quality of bluebunch wheatgrass (Pseudoroegneria spicata) and Idaho fescue (Festuca idahoensis) over the course of the dormant season and in response to concurrent environmental conditions. We collected forage samples every 14 days for two consecutive winters in southwestern Montana, USA. Samples were analyzed for crude protein (CP), acid detergent fiber (ADF), and neutral detergent fiber (NDF). A suite of environmental metrics was derived from PRISM weather data. Data were analyzed with a linear mixed model and the STATICO ordination method. Crude protein and ADF varied throughout the winter across both years, with CP ranging from 1.9–4.0% and ADF from 37–42%. The differences between species were more pronounced and more consistent in CP. The differences between years were more pronounced in ADF and NDF. Relative temperature explained the most variation in forage quality. Crude protein is positively correlated with short-term warmer temperatures, whereas NDF is positively correlated with longer-term warmer temperatures. This demonstrates that forage quality can change over the dormant season and is influenced by winter weather events.