Archive:000/Limits to sustainable animal consumption

Farming

• Vegans rightly point out that meat-containing diets require more land (and thus more deforestation). Feeding crops to animals is a net loss of protein and calories. But...
• Pro-meat folks rightly point out that some land is only suited for grazing animals. And unlike humans, cows can live on eating grass(...)( and so can buffalo, sheep and goats. But chickens & pigs can't. ).

This raises a more important question:

If farm animals only ever ate...

• grasses and other plants from pasture & range (...)( especially from biodiverse natural lands that keep a lot of carbon stored in the roots of plants ), and
• the parts of food crops that humans can't eat (...)( for example corn cobs after the kernels have been removed (ruminants can digest certain kinds of fibrous matter that other species can't) ),

and never...

• human-edible food crops (...)( including corn and soy as those could be made into flour ) (...)( Grey area: Perhaps also include "spent grains" and "fryer waste oil" because the original materials were human-edible, and the downgrading was a choice ), nor
• crops grown specifically for animal feed (...)( Grey area: Perhaps also include the more superficial types of "pasture" that are monoculture-like and don't keep a lot of permanent roots. The exact definition can be specified in the answer to the question. ),

how much animal protein (...)( from meat, milk and/or eggs etc ) could be produced?

Clearly it's less than the status quo, as there are fewer sources of feed. But how much less?

Estimate

About 12 grams of animal protein per day, per capita, globally.
This includes both meat and dairy, from all animals (ruminants).

See mathsSee maths

pasture

2.8 billion tonnes/year

Dry mass of all grass & leaves, grazed from all pasture land

Source:

Breewood, H. & Garnett, T. (2020). What is feed-food competition? (Foodsource: building blocks). Food Climate Research Network, University of Oxford.
Page 10
References primary source:
Mottet, A., de Haan, C., Falcucci, A., Tempio, G., Opio, C., & Gerber, P. (2017). Livestock: On our plates or eating at our table? A new analysis of the feed/food debate. Global Food Security.

residues

1.7 billion tonnes/year

Dry mass of all crop residues, byproducts, and oilseed cakes except for soybean

This should be, in principle, all the human-inedible parts of food crops (inedible due to being too fibrous; ruminants can digest the fiber and get calories from it).
Soybean meal is not counted here, because it can be turned into human food (soy flour).

Source:
Breewood, H. & Garnett, T. (2020). What is feed-food competition? (Foodsource: building blocks). Food Climate Research Network, University of Oxford.
Page 10
References primary source:
Mottet, A., de Haan, C., Falcucci, A., Tempio, G., Opio, C., & Gerber, P. (2017). Livestock: On our plates or eating at our table? A new analysis of the feed/food debate. Global Food Security.

conversion_ratio

133

Ruminants produce 1 gram of human-edible protein for every 133 grams of dry matter they eat.

Dry matter includes all materials eaten by ruminants (both human-edible and human-inedible).

Source:
Mottet, A., de Haan, C., Falcucci, A., Tempio, G., Opio, C., & Gerber, P. (2017). Livestock: On our plates or eating at our table? A new analysis of the feed/food debate. Global Food Security.
The number is mentioned in the Abstract: https://www.tabledebates.org/research-library/livestock-our-plates-or-eating-our-table

world.population

8 billion

(pasture + residues) / conversion_ratio (grams/day per capita)(world.population) (calculation loading) ^ Total amount of protein from both meat and dairy, combined. (...)( This is probably a slight overestimate, because feed efficiency ratios are lower when the cows are fed less human-edible grains. )

This is less than the status quo, because the animals wouldn't be fed corn grain or soybean meal(...)( nor anything else that could have been turned into food for humans. Corn grain can be ground into corn flour (for tortillas etc) and soybean meal can be ground into soy flour and used in baked goods to improve protein & texture. It can also be used for making soy protein isolate (supplements, imitation meats, etc). ).

Status quo

Ruminants (cows, buffalo, goats and sheep) produce a total of about 16 grams of protein per day per capita globally.

• 10 g protein/day from milk(...)( from 297 mL/day of milk ) per capita
• 6 g protein/day from meat(...)( from 30 g/day of meat ) per capita
• This was calculated in Code:food2.sql.

Some of this food goes to waste unfortunately, but there might be ways to mitigate that problem.

Grass-fed animal production can't really increase without destroying forests and other wildlife, because most of the world's farmland is already pasture, and that's not even counting rangelands.

Hunting

Hunter-gatherer lifestyles were sustainable in prehistoric times when the world population was less than 0.1 billion - today we are at 8.0 billion. Hunting might be a great survival tactic if you're lost in the woods. But it's not going to feed the world. There would be mass extinctions of wild animals if we tried.

Fishing

Wild-caught fish could provide 5 or 6 grams/day of protein per capita globally, if none of it was wasted.

See mathsSee maths

seafood.production.wild

93 million tonnes/year

Global production of wild-caught fish and other seafood (not farmed)

Includes bones.
Using most recent data available.
Fishing grew a lot from 1960 to 1990 but (unlike fish farming) has not increased since 1995. This suggests that we've reached the ecological limit.

https://ourworldindata.org/fish-and-overfishing

fish.protein

18%

Protein content of fish (divided by total mass including bones)

world.population

8 billion

Number of people alive today, globally

https://www.unfpa.org/data/world-population-dashboard
Last updated in 2023

Grams of fish: seafood.production.wild (g/day per capita)(world.population) (calculation loading) Grams of protein: seafood.production.wild * fish.protein (g/day per capita)(world.population) (calculation loading)

The sustainable level of consumption might be a bit less than this, because overfishing is still an issue.

The rest of fish is farmed, which, as mentioned earlier, is a net loss of protein. Farmed fish are fed food crops that humans could otherwise eat.