Elevation of mean air temperature related to climate change speeds up plant maturity, which influences mostly forage feed value. The objective of the study was to assess variation in hay quality harvested over 32 years at the same experimental site, and whether feed value is better predicted by combining agro‐climatic variables with chemical composition. From 1979 to 2010, the in vivo digestibility (OMd) and voluntary dry matter intake (VDMI) of 271 hays, harvested during the first vegetation cycle on permanent grasslands, were measured in sheep. Over 32 years, the mean air temperature between February and August increased significantly by 1.34°C. Cutting date was advanced by 6 days, but the average sum of temperature at cutting (ST) increased significantly by 13%. Crude protein (CP) content declined (−22%, p < .001), crude fibre content increased (+8%, p < .001), OMd decreased (−3%, p = .012) and VDMI increased (+9%, p = .011). Changes in the chemical composition and OMd were consistent with the increase in ST. Finally, the prediction of OMd from CP and crude fibre contents (R² = .57, RMSE = 2.99) was slightly improved by the addition of ST and hay drying time (R² = .60, RMSE = 2.83). Climate change may have a negative indirect effect on hay quality if an earlier cutting date does not compensate for its effect on the faster maturation of the plants. Moreover, agro‐climatic criteria could help to monitor and predict hay quality in relation to intra‐ and inter‐annual climatic changes.

中文翻译：

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永久性高山草场干草的长期演变和饲料价值预测：与气候变化有关的32年数据集的分析

与气候变化有关的平均气温的升高加快了植物的成熟，这主要影响了饲草饲料的价值。该研究的目的是评估在同一实验地点32年内收获的干草质量的变化，以及通过结合农业气候变量和化学成分来更好地预测饲料价值。从1979年到2010年，在绵羊的永久植被的第一个植被周期中收获了271干草的体内消化率（OMd）和自愿摄入的干物质（VDMI）。在过去的32年中，2月至8月的平均气温显着提高了1.34°C。切割日期提前了6天，但是切割时的平均温度（ST）显着提高了13％。粗蛋白（CP）含量下降（−22％，p <.001），粗纤维含量增加（+ 8％，p  <.001），OMd减少（-3％，p  = .012）和VDMI增加（+ 9％，p  = .011）。化学成分和OMd的变化与ST的增加一致。最后， 通过添加ST和干草干燥时间（R ²  = 0.60，RMSE = 2.83），从CP和粗纤维含量（R ² = .57，RMSE = 2.99）对OMd的预测略有改善。如果较早的砍伐日期不能弥补其对植物更快成熟的影响，那么气候变化可能会对干草质量产生间接的负面影响。此外，农业气候标准可以帮助监测和预测与年内和年际气候变化有关的干草质量。