Department of Animal and Poultry Science, Virginia Tech, Blacksburg, VA 24060.
U.S. Dairy Forage Research Center, USDA-ARS, Madison, WI 53706.
J Dairy Sci. 2020 Nov;103(11):10867-10881. doi: 10.3168/jds.2020-18570.
Questions regarding the balance between the contribution to human nutrition and the environmental impact of livestock food products rarely evaluate specific species or how to accomplish the recommended depopulation. The objective of this study was to assess current contributions of the US dairy industry to the supply of nutrients and environmental impact, characterize potential impacts of alternative land use for land previously used for crops for dairy cattle, and evaluate the impacts of these approaches on US dairy herd depopulation. We modeled 3 scenarios to reflect different sets of assumptions for how and why to remove dairy cattle from the US food production system coupled with 4 land-use strategies for the potential newly available land previously cropped for dairy feed. Scenarios also differed in assumptions of how to repurpose land previously used to grow grain for dairy cows. The current system provides sufficient fluid milk to meet the annual energy, protein, and calcium requirements of 71.2, 169, and 254 million people, respectively. Vitamins supplied by dairy products also make up a high proportion of total domestic supplies from foods, with dairy providing 39% of the vitamin A, 54% of the vitamin D, 47% of the riboflavin, 57% of the vitamin B, and 29% of the choline available for human consumption in the United States. Retiring (maintaining animals without milk harvesting) dairy cattle under their current management resulted in no change in absolute greenhouse gas emissions (GHGE) relative to the current production system. Both depopulation and retirement to pasture resulted in modest reductions (6.8-12.0%) in GHGE relative to the current agricultural system. Most dairy cow removal scenarios reduced availability of essential micronutrients such as α-linolenic acid, Ca, and vitamins A, D, B, and choline. Those removal scenarios that did not reduce micronutrient availability also did not improve GHGE relative to the current production system. These results suggest that removal of dairy cattle to reduce GHGE without reducing the supply of the most limiting nutrients to the population would be difficult.
关于家畜食品对人类营养的贡献与环境影响之间平衡的问题，很少有研究评估特定物种或如何实现建议的减畜。本研究的目的是评估美国乳制品行业目前对营养供应和环境影响的贡献，描述替代以前用于奶牛养殖的土地用途对土地的潜在影响，并评估这些方法对美国奶牛养殖数量减少的影响。我们构建了 3 种情景来反映从美国食品生产系统中移除奶牛的方式和原因的不同假设，以及 4 种以前种植奶牛饲料的土地的潜在新用途的土地利用战略。情景在如何重新利用以前用于饲养奶牛的谷物的土地方面也存在假设差异。当前系统提供了足够的液态奶，以满足分别为 7120 万人、1690 万人和 2540 万人提供的年度能量、蛋白质和钙需求。乳制品提供的维生素也构成了国内食品供应总量的很大一部分，其中乳制品提供了 39%的维生素 A、54%的维生素 D、47%的核黄素、57%的维生素 B 和 29%的胆碱，供美国人食用。在当前的管理下，退休（不产奶但保留奶牛）奶牛不会导致绝对温室气体排放量（GHGE）相对于当前生产系统发生变化。与当前农业系统相比，减少奶牛数量和将其退休到牧场都导致 GHGE 适度减少（6.8-12.0%）。大多数奶牛移除情景减少了必需微量营养素的供应，如α-亚麻酸、钙和维生素 A、D、B 和胆碱。那些没有减少微量营养素供应的移除情景也没有相对于当前生产系统改善 GHGE。这些结果表明，在不减少对人口最具限制作用的营养素供应的情况下，为减少 GHGE 而减少奶牛数量将是困难的。
