That absolute statement is absolutely false. Say, I have a chicken that can be feed from left-over bread or wheat. I can store the wheat basically indefinitely, so there is no spoilage. Also, I cannot use wheat directly, so it is unusable calories for me. But I cannot store bread for very long, so there is spoilage. Now, using the chicken, I can convert the spoiled bread into eggs and meat, useful calories for me.

Say 10% of the calories produced for me at a human go to waste. And I can convert them at 25% efficiency to usable calories via a chicken. Then I have just increased the yield of usable calories by 2.5%. In consequence, I need to buy less and thus emissions can be reduced.

Bread typically becomes "stale" (texture change due to internal moisture redistribution) before it spoils (usually by mold growth). Stale bread is still edible, and there are recipes that prefer it over fresh bread, e.g. bread pudding and bread sauce. It does not have to be fed to chickens to avoid wasting it.

And wheat can be converted to pasta, which can be stored for years, and can be easily made edible by brief cooking. You can reduce wastage of wheat to negligible levels, and chicken farming has non-zero overhead, so it seems unlikely that the chickens are an efficiency win if you take reasonable care.

It's pretty reductionist to look at this from a pure calorie input / output point of view. Keeping a few pastured chickens to feed food waste can provide pest control in a garden, an additional source of nutrition for people (which is a complete protein) and a rich fertilizer from their waste.

> In consequence, I need to buy less and thus emissions can be reduced.

You're not taking into account that, by virtue of being an animal taking in oxygen and creating carbon dioxide / other pollutants, the chicken itself is contributing to greenhouse gas emissions.

The question is, in real life, are the bonus calories we get from animal farming efficient enough so as to be worth those greenhouse gases? Given the massive GHG emissions of animal agriculture, it doesn't seem so.

Perhaps I'm misunderstanding your example, though: feedback appreciated

Of course there is. Keeping a couple of goats that live off a natural pasture provides calories for humans that otherwise would have to be provided by something else. Keeping a pig that mostly lives off food waste has a similar effect.

Planting something that you can eat directly for the calories on that land area would be better (or don't touch it and let it sequester carbon, and plant somewhere else that's more suited).

If you feed the goat 100 calories, there is no way you get back 100 calories.

Many areas can sustain goats but can't sustain agriculture. Goats can also eat stuff that is inedible to humans, for example the parts of wheat an corn that are not the grains. A lot of plant matter that has zero calories for humans has >0 calories for ruminants.

Commercial grazing tends to overgraze which is worse in the long run.

Sustainable meat production is probably extremely far from commercially viable.

@adrianN: You are talking about what is called marginal land in agriculture and environmental science. Recent research shows that even marginal land has a better GHG balance when left untouched and not grazed by livestock

It's always better plant and eat the food directly than to feed it to an animal.

Of course, if you're in a scenario where you live on a small island with no connection to the outside world, and you only have marginal land, yes, you need might need to have livestock to survive. But that's not what we're talking about here.

Of course marginal land which is left untouched has no monetary or food value. What is the value of the difference between grazed and ungrazed? Is it enough to justify paying people to leave it fallow?

That is interesting. Do you have a link to that research?

Here's a good study on carbon opportunity cost of land: https://www.nature.com/articles/s41893-020-00603-4.epdf?shar...

Thank you!

Which do you think affects GHG emission more? A rich grassland with multiple feet of biologically active, carbon rich soil, or a desert? Proper herd grazing is a part of healthy grasslands as the animals trample plants and poop everywhere before moving to a new area to graze, creating plenty of soil.