While considerable research has quantified effects of grazing management and precipitation on plant communities, less is known about how seasonal effects influence extrusa diet quality selected by grazing ruminants. We tested effects of cattle grazing to two residual herbages (600 kg [moderate] or 300 kg [low] animal unit mo [AUM]/ha) and two grazing seasons (summer and fall) on 20 indicators of ruminant extrusa diet quality over a 6-yr period. We found no effect of residual herbage on 13 indicators of diet extrusa quality (P ≥ 0.13) and no effect of season on 4 indicators of extrusa diet quality (P ≥ 0.0773). We did, however, detect effects of yr on extrusa diet quality metrics and nutrients, likely due to variation in annual precipitation, which ranged from 63.9% to 138.6% of the long-term average. Most noticeably, the mineral Mn in extrusa was substantially lower in yrs with higher precipitation (P < 0.0001). While grazing intensity had divergent effects on forage quality in the summer versus fall, annual precipitation was often important. Crude protein was lowest in fall of 2013 (6.5%) and 2018 (7.78%), two high-precipitation yrs, but it was also low in fall of 2015 (7.30%), a low-precipitation yr (P < 0.0001). Forage extrusa Cu, an important catalyst in ruminant metabolism, exhibited a yr × season interaction. Copper in fall of 2018 was greater compared with all other yrs and seasons in the study (P < 0.0001), 35.7% greater than summer of 2018, a high-precipitation yr, and 82.9% and 43.5% greater than summer and fall of 2013, another high-precipitation yr. Seasonal variation in diet nutrients and quality indicators were complex and complicated by yr effects, which sometimes related to precipitation amounts.

虽然大量研究量化了放牧管理和降水对植物群落的影响，但对季节性影响如何影响放牧反刍动物选择的 extrusa 饮食质量知之甚少。我们测试了放牧对两种残留牧草（600 kg [中等] 或 300 kg [低] 动物单位 mo [AUM]/ha）和两个放牧季节（夏季和秋季）对反刍动物饲料质量的 20 项指标的影响。 6 年期。我们发现饮食extrusa质量（13个指标无残留牧草的效果P ≥0.13）和季节对extrusa饮食质量的4个指标没有影响（P≥ 0.0773)。然而，我们确实检测到 yr 对 extrusa 饮食质量指标和营养素的影响，可能是由于年降水量的变化，其范围为长期平均值的 63.9% 至 138.6%。最值得注意的是，随着沉淀的增多，挤出物中的矿物 Mn 在几年内显着降低（P < 0.0001）。虽然放牧强度对夏季和秋季的牧草质量有不同的影响，但年降水量通常很重要。粗蛋白在 2013 年秋季（6.5%）和 2018 年（7.78%）两个高降水年最低，但在 2015 年秋季（7.30%）低降水年（P< 0.0001)。饲料挤出物铜是反刍动物代谢的重要催化剂，表现出年×季节的相互作用。与研究中的所有其他年份和季节相比，2018 年秋季的铜含量更高 ( P < 0.0001)，比 2018 年夏季高 35.7%，这是高降水年，比 2013 年夏季和秋季高 82.9% 和 43.5% ，又一个高降水年。日粮营养素和质量指标的季节性变化因年份效应而变得复杂，有时与降水量有关。