Our World in Data provides a breakdown of global land use, represented in the following graph. Of the 29% of the earth’s surface that is land, 76% is classified as habitable of which agriculture utilises 45%, or 48m km2. In this representation the broad association of land associated with livestock – some 38m km2, 6m km2 of which is designated as growing crops for livestock feed – and the 83% proportion of calories delivered for human use by plant-based food produced on 16% of agricultural land relative to the 17% livestock calorie component that utilised 80% of agricultural land demands explanation as does the equivalent human protein proportions of 62% from plants and 38% from livestock. These proportions and numbers are widely misunderstood and misrepresented.
Firstly all land is not equal: The vast majority of the 32m km2 of grazing lands, 67% of all agricultural land, cannot be cropped as they are characterised by extreme mountainous or rough topography, low and erratic rainfall and temperature extremes, and in many cases highly degraded or low fertility soils. Consequently any human food produced by livestock off this huge area is food that would not be otherwise available. Secondly herbivores, which include ruminant livestock, over millennia have developed the unique ability to utilise high cellulose content grasses and shrubs for growth and production, thereby transforming human inedible biomass into nutrient dense milk, meat and fibre, with animal sourced foods also intimately related to the evolution of the human species. Unsurprisingly given the evolutionary linkage these foods are highly bioavailable and contain nutrient ratios ideal for the human diet.
The evolutionary wheel also includes complementary links between herds of grazed livestock and the landscape, soils and herbage that they graze. Thousands of years of grazing by undomesticated herds of bison, antelope, deer, large game animals and megafauna have returned manure to encourage plant growth, disturbed the soil to incorporate it and encouraged regrowth by removing the upper leaves and stems which in turn returned carbon to the soil, improved biodiversity of above and below ground species and improved soil water holding capacities, reducing the impact of droughts and floods. Contemporary regenerative grazing practices apply these same processes to restore degraded soils and landscapes. Thirdly, the proteins in milk and meat are more bioavailable and contain a superior range of essential amino acids, iron, zinc, Vitamin B12 and other micronutrients than do most plant proteins so that the weight and proportions of bioavailable nutrients provided by animal sourced foods is far higher than the proportions of tonne of animal and plant material harvested or consumed. Also, not explicit in these data is the fact that continuous cropping is not possible on a high percentage of cropping land which is managed in rotations with a pasture rest phase in many regions, with soil fertility and structure improved by grazing during the pasture phase with manure, including that from intensive animal systems, reducing or replacing the use of synthetic fertilizers.
A further consideration is that crops also contain a high proportion of human inedible material that can be utilised by livestock. This includes stalks, leaves and hulls removed or left standing during harvesting or packing, together with many byproducts such as beet pulp, whole cottonseed, brewers and distillers grains together with weather damaged grains and oilseed meals that are recycled through livestock.
The net result is that an estimated 86% of global livestock diets is material not edible by humans. Due to this proportion the amount of human edible food produced through intensive livestock systems can often exceed the smaller amount of human edible material within their diets.
