Data from: Continental-scale patterns reveal potential for warming-induced shifts in cattle diet

In North America, it has been shown that cattle in warmer, drier grasslands have lower quality diets than those cattle grazing cooler, wetter grasslands, which suggests warming will increase nutritional stress and reduce weight gain. Yet, little is known about how the plant species that comprise cattle diets change across these gradients and whether these shifts in dietary quality coincide with shifts in dietary composition, i.e. the relative abundance of different plant species consumed by cattle. To quantify geographic patterns in dietary composition, we analyzed the dietary composition and dietary quality of unsupplemented cattle from 289 sites across the central US by sequence-based analyses of plant DNA isolated from cattle fecal samples. Overall, assuming that the percentage of reads for a species in a sample corresponds to the percentage of protein derived from the species, only 45% of the protein intake for cattle was derived from grasses. Within the Great Plains, northern cattle relied more on grasses than southern cattle, which derived a greater proportion of their protein from herbaceous and woody eudicots. Eastern cattle were also more likely to consume a unique assemblage of plant species than western cattle. High dietary protein was not strongly tied to consumption of any specific plant species, which suggests that efforts to promote individual plant species may not easily remedy protein deficiencies. A few plant species were consistently associated with lower quality diets. For example, the diets of cattle with high amounts of Elymus or Hesperostipa were more likely to have lower crude protein concentrations than diets with less of these grasses. Overall, our analyses suggest that climatic warming will increase the reliance of cattle on eudicots as protein concentrations of grasses decline. Monitoring cattle diet with this DNA-based sequencing approach can be an effective tool for quantifying cattle diet to better increase animal performance and guide mitigation strategies to changing climates.

已有研究表明，在北美地区，相较于采食凉爽湿润草原的牛只，温暖干旱草原中的牛只日粮品质更低，这意味着气候变暖会加剧牛只的营养胁迫并降低其增重效率。然而，目前对于构成牛只日粮的植物物种如何随环境梯度变化，以及日粮品质的变化是否与日粮组成（即牛只采食的不同植物物种的相对丰度）的变化同步，尚不清楚。为量化日粮组成的地理分布模式，本研究通过对牛只粪便样本中分离得到的植物DNA进行测序分析，对美国中部289个采样点的未补饲牛只的日粮组成与日粮品质进行了分析。总体而言，假设样本中某物种的测序读段（reads）占比对应该物种贡献的蛋白质占比，牛只的蛋白质摄入仅45%来自禾本科植物。在大平原区域，北部牛只比南部牛只更多依赖禾本科植物，而南部牛只的蛋白质更多来自草本和木本真双子叶植物（eudicots）。东部牛只相较于西部牛只，更倾向于采食独特的植物物种组合。高日粮蛋白水平与任何特定植物物种的采食并无显著关联，这表明通过推广单一植物物种来改善牛只蛋白质缺乏的策略可能难以奏效。部分植物物种始终与低品质日粮相关联。例如，采食大量披碱草属（Elymus）或异针茅属（Hesperostipa）的牛只，其日粮的粗蛋白浓度往往低于采食较少该类禾草的牛只。总体而言，本研究的分析结果表明，随着禾本科植物的蛋白质浓度下降，气候变暖将使牛只更依赖真双子叶植物（eudicots）。通过这种基于DNA测序的方法监测牛只日粮，可作为量化牛只日粮的有效工具，从而更好地提升动物生产性能，并为应对气候变化制定减缓策略提供指导。