Data from: Long-term declines in dietary nutritional quality for North American cattle

With over 1 billion cattle in the world as well as over 2 billion sheep, goats and buffalo, these animals contribute approximately 15% of the global human protein supply while producing a significant proportion of anthropogenic emissions of greenhouse gases and global nutrient fluxes. Despite increasing reliance on grazers for protein production globally, the future of grazers in a changing world is uncertain. Factors such as increased prevalence of drought, rising atmospheric CO2 concentrations, and sustained nutrient export all have the potential to reduce cattle performance by reducing the nutritional quality of forage. However, there are no analyses to quantify changes in diet quality, subsequent impact on cattle performance and cost of supplementation necessary to mitigate any predicted protein deficiency. To quantify the trajectory of nutritional stress in cattle, we examined more than 36 000 measurements of dietary quality taken over 22 yr for US cattle. Here, we show that standardizing for spatial and temporal variation in drought and its effects on forage quality, cattle have been becoming increasingly stressed for protein over the past two decades, likely reducing cattle weight gain. In economic terms, the replacement costs of reduced protein provision to US cattle are estimated to be the equivalent of $1.9 B annually. Given these trends, nitrogen enrichment of grasslands might be necessary if further reduction in protein content of forages is to be prevented.全球肉牛存栏量超10亿头，绵羊、山羊与水牛的总存栏量超20亿。这类家畜不仅为全球人类提供了约15%的蛋白质供给，同时也是人为温室气体排放与全球营养物质循环通量的重要组成部分。尽管全球范围内对放牧家畜作为蛋白质来源的依赖度持续攀升，但在气候变化的大背景下，放牧家畜的未来走向仍存在不确定性。诸如干旱频发、大气CO₂浓度升高以及持续的养分输出等诸多因素，均可能通过降低牧草的营养品质，进而削弱肉牛的生产性能。然而目前尚无相关分析能够量化饲粮营养品质的变化、其对肉牛生产性能的后续影响，以及缓解预估蛋白质缺乏所需的补饲成本。为量化肉牛的营养胁迫变化轨迹，我们分析了过去22年间针对美国肉牛收集的超3.6万份饲粮品质检测数据。本研究通过校正干旱及其对牧草品质影响的时空变异后发现，在过去二十年间，肉牛面临的蛋白质营养胁迫程度持续加剧，这大概率会降低肉牛的增重效率。从经济维度来看，美国肉牛因蛋白质供给不足所需的补饲替代成本，年均约合19亿美元。基于上述趋势，若要阻止牧草蛋白含量进一步下降，或需对草原实施氮肥富集改良措施。