Predicting the effect of climate change on grassland yields necessitates considering the potential interactions with grassland management. Our 42 years of data from a permanent grassland managed at two fertilizer regimes (PK or NPK) and two defoliation frequencies (two or three cuts a year) give insight into such interactions. The site is located in the Swiss Jura Mountains at 930 m a.s.l. At this site, mean air temperature has risen by 2°C over the last 42 years, while annual rainfalls did not change significantly. Considering the water deficit during the vegetation period (March-October) allowed to account for one third of the large interannual yield variability (coefficient of variation 18%). Over the 42-year period, yields decreased by an average of 24% under the 3-cut but held steady under the 2-cut treatments. The yield decrease under more frequent defoliation cannot be explained by nutrient depletion, nor by a degradation of the botanical composition compared to the 2-cut treatments. A similar yield evolution over the decades was observed for all harvests of the year, without difference between the spring and the summer harvests. In conclusion, 42 years of data show that the frequency of defoliation may influence long-term grassland resilience to rise in temperature.