This study was aimed at analyzing changes in botanical and chemical composition, and in vitro rumen fermentation characteristics of an upland grassland exposed to climate changes in controlled conditions except for light intensity, which was the natural one. Grassland was exposed to future climate scenario coupled with CO2 treatments (390 and 520 ppm) from the beginning of spring. During summer, an extreme event (two weeks of increased temperature, +6 °C, associated with severe drought, ECE) was associated. After the ECE, a recovery treatment was performed. Three cutting dates in April, June and November were considered. Our results indicate that increases in greenness, nitrogen (N) content and changes in water-soluble carbohydrate profile for the cut of November result in higher in vitro dry matter degradability (IVDMD) in the rumen. The neutral detergent fiber : nitrogen (NDF : N) ratio appeared to be a main driver of forage quality affected in opposite ways by elevated CO2 and ECE, with a strong impact on rumen fermentation. A trend towards an interaction between atmospheric CO2 concentration and ECE was observed in IVDMD, indicating that their effects could partly offset each other. These findings indicate that the different factors of climate change have to be considered together to characterize their effects on forage quality and use by ruminants.
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Niderkorn et al. (2021) studied this question.