Research press release


Nature Ecology & Evolution

Is a sustainable US beef industry possible?


米国の牛肉産業は、牛そのものばかりではなく、牛に与えるために栽培される飼料からも、有数の温室効果ガス排出者として挙げられることが多い。今回、Gidon Eshel、Ron Miloたちは、持続可能な牛肉生産について、「草地(牧草および現地でベール化された少量の干し草)、およびモルトフィード(ウイスキーかす)やビートパルプ(砂糖大根かす)などの食品工業副産物で肥育された牛」と定義した。



関連するNews & Views記事では、Les Firbankが「(著者たちは)最終的な推定が大胆な仮定と予備的なデータに基づくものであることを認めているが、その論理的で透明性のある枠組みは、計算を全国規模で行うことを可能にし、政策の再構成に向けた現実的な取り組みを行うものである」と述べている。

A model for the more sustainable supply of up to 45% of current US beef consumption is presented in a paper published online this week in Nature Ecology & Evolution. The study also suggests that, if Americans halved their weekly beef consumption, the US beef industry could potentially become environmentally sustainable.

The US beef industry is often cited as a major greenhouse gas contributor, not only from the cattle themselves, but also from the fodder grown to feed them. Here, Gidon Eshel, Ron Milo and colleagues define sustainable beef production as cattle that are raised on grassland (pasture and small amounts of locally baled hay) and food industry by-products, such as distillers’ grains or sugar-beet pulp.

The authors' model finds that, using this definition of sustainable beef production, an estimated 32 million hectares of cropland currently used to grow fodder could be reallocated for plant-based food production. They suggest that this reallocation would also dramatically reduce nitrogen fertilizer and irrigation water use, while also substantially reducing greenhouse gas emissions. The authors find that combining the change in land use with pasturing could lead to 45% of current beef production being sustainable. In addition, they find that halving the size of existing pastureland used (to about 135 million ha), by abandoning less productive grasslands, can still sustainably deliver 43% of current production.

Finally, they show that a reduction in beef consumption from the current level of about 460 g per person per week to about 200 g per person per week could make the entire US beef industry environmentally sustainable (by the narrow definition of the paper). The authors emphasize that this is just one possible model and definition of sustainability, and also caution that any model must maintain protein needs. However, due to the very low feed-to-food protein conversion efficiency of beef, reallocating feed land to all considered plant alternatives at least maintains protein supply, and reallocation to such protein-rich plants as soybean, for example, increases protein production from the land five-fold.

In an accompanying News & Views, Les Firbank writes: "[The authors] admit that their final estimations are based on heroic assumptions and preliminary data, but their logical, transparent framework permits calculations to be made on the national scale, and makes a real effort at re-imagining policy."

doi: 10.1038/s41559-017-0390-5

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