Craine Joseph M, Angerer Jay P, Elmore Andrew, Fierer Noah
Jonah Ventures, Manhattan, KS, United States of America.
Texas A&M Agrilife Research, Blackland Research and Extension Center, Temple, TX, United States of America.
PLoS One. 2016 Aug 23;11(8):e0161511. doi: 10.1371/journal.pone.0161511. eCollection 2016.
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.
在北美，研究表明，在温暖、干燥草原上的牛所食用的饲料质量低于在凉爽、湿润草原上放牧的牛，这表明气候变暖将增加营养压力并减少体重增加。然而，对于构成牛饲料的植物物种如何在这些梯度上变化，以及饲料质量的这些变化是否与饲料组成的变化相一致，即牛所食用的不同植物物种的相对丰度，人们了解甚少。为了量化饲料组成的地理模式，我们通过对从牛粪便样本中分离的植物DNA进行基于序列的分析，分析了美国中部289个地点未补充饲料的牛的饲料组成和饲料质量。总体而言，假设样本中某一物种的读数百分比对应于该物种提供的蛋白质百分比，牛摄入的蛋白质中只有45%来自禾本科植物。在大平原地区，北部的牛比南部的牛更依赖禾本科植物，而南部的牛从草本和木本双子叶植物中获取的蛋白质比例更高。东部的牛也比西部的牛更有可能食用独特的植物物种组合。高饲料蛋白质与食用任何特定植物物种的关联并不紧密，这表明推广单一植物物种的努力可能无法轻易弥补蛋白质缺乏问题。一些植物物种始终与较低质量的饲料相关。例如，含有大量披碱草或针茅属植物的牛饲料，其粗蛋白浓度比含有较少这些禾本科植物的饲料更有可能更低。总体而言，我们的分析表明，随着禾本科植物蛋白质浓度下降，气候变暖将增加牛对双子叶植物的依赖。用这种基于DNA的测序方法监测牛的饮食，可以成为量化牛饮食的有效工具，以更好地提高动物性能并指导应对气候变化的缓解策略。
