Limiting livestock production to pasture and by-products in a search for sustainable diets
研究设计了一种基于全球人均可耕地限制的“公平”饮食方法，以瑞典为例，评估三种畜牧业场景（利用牧草和副产品）下饮食的环境影响，发现所有方案均超出气候和氮磷边界。
A method was developed for designing ‘fair’ diets (not using more than globally available arable land per capita) and for assessing the sustainability of such diets. The diets were based on the principle of ‘ecological leftovers’ for livestock production, i.e. raising livestock on pasture and by-products not suitable for or wanted by humans. The method was applied to Sweden using three different scenarios for livestock production, all taking the starting point that semi-natural pastures should be grazed by ruminants for reasons of biodiversity conservation. The scenarios also included differing use of by-products (from crop production and food processing) to either boost milk production (I-Milk scenario) or produce eggs and pig meat (E-Milk and Suckler scenarios). In I-Milk, milk and meat were produced in intensive systems in which dairy cows and their offspring only grazed to a limited extent, resulting in the human diet containing recommended levels of dairy products (350 ml milk per day) and meat twice a week. Milk could also be exported. In E-Milk, pasture was used more for dairy cows and their offspring, resulting in fewer animals and less milk (150 ml milk per day) and four servings of meat per week. In the Suckler scenario, pasture was grazed by suckler herds providing no milk but meat four times per week. The environmental impacts of the diets were assessed using the planetary boundaries framework. The results showed substantially lower environmental impacts compared with the average current Swedish diet, but the strict absolute climate boundary and the N and P input boundaries were still exceeded for all diets. The approach adopted, of letting the ecological resource capacity act as the constraining factor for livestock production, is in line with agroecology principles and efficient use of land to improve food security, and could be useful in discussions about sustainable consumption of animal products.