Effects of elevated CO<sub>2</sub> and extreme climatic events on forage quality and in vitro rumen fermentation in permanent grassland

Abstract. The aim of this study was to analyze changes in botanical and chemical composition, as well vitro rumen fermentation characteristics an upland grassland exposed climate controlled CO2 concentration, air temperature precipitation conditions. Grassland a future scenario coupled with treatments (390 520 ppm) from the beginning spring. During summer, extreme climatic event (ECE; 2 weeks +6 ∘C increase temperature, together severe drought) applied then followed by recovery period. Three cutting dates were considered, i.e. April, June November. results indicate that increases greenness, nitrogen (N) content water-soluble carbohydrate profile association composition for November cut lead higher dry matter degradability (IVDMD) rumen. neutral detergent fiber : (NDF:N) ratio appeared be key driver forage quality, which affected opposite ways elevated ECE, strong impact on fermentation. Atmospheric concentration interaction ECE tended affect IVDMD, indicating effects may partly offset each other. Our findings various factors change need considered order properly characterize their quality use ruminants.