Per leathers: one, we don't have to completely eliminate cattle. Two, synthetics exist. Three, alternatives are being made/investigated [1].
[0] https://en.wikipedia.org/wiki/Dovecote [1] https://www.felsie.co.uk/ (and others, if you google around)
However, I think this is another example of something that is 'just too small to matter' in terms of feeding the world's population today. Often I see 'nice' stories about e.g. using human waste to fertilise fields, that quite frankly do not (usually) scale at all well. We (UK) use tractors to shovel and spread manure - 10s, 100s of tons of the stuff - a dovecote or 10 really isn't going to help, and certainly won't be economic.
It seems a bit like someone telling me I should use an abacus to increase my compute power - 'they were a good idea in the past, why aren't you using them now?'
We feed a lot of grains to aninals as feed. That food coupd be used to feed people. We could certainly downsize meat producting by 70% withiit any adverse impacts -most people eat way too mich meat
If you reduce meat production, you'll hike up prices, likely pricing out those with autoimmune diseases that barely survive already. So technically you are true like in "you can still eat meat in theory", but in practice those folks won't be able. Now where is the good faith in that argument?
You're saying a lot of stuff and I'm going to need more evidence to be convinced as to your position. For what reason would meat prices increase if people ate less meat?
You are right that it can be done badly, as can many other things. I'd say you are actually arguing against badly regulated animal farming (especially since you mention the US), rather than animal farming per se.
You'd need to cite some sources for that. And explain where the millions of tons of animal manure go.
Here in Northern Europe 100% of manure from housed animals is used, either spread as manure or, increasingly, used for biomethane
That's the wrong statistics to look it - 100% of waste coffee is used. They already have it, good management will figure out a way to use it.
But you cannot make an argument that we have to keep drinking coffee because fertiliser industry will collapse without waste coffee.
There are thousands of studies about impacts of intensive animal faming on landscape, economy, health and society in general, they are all negative. This was settled like 40 years ago.
You said
> Only a small percentage of manure is reused as fertiliser because transporting it is expensive, and messy
That's straight up false, for Northern Europe anyway.
I think in my area they try to use manure to produce methane.
Source? Preferably reputable
Compost can help. I don't know how much that would scale in any case.
Is true that we can produce some fertilizers chemically, but we need to invest huge amounts of energy for this; After Wikipedia >1% of all the energy that we humans use in the planet is spent just to make ammonia, and many of this is used to make urea. If I'm not wrong we need also natural gas to feed the process, so this energy came basically from non renewables. Is part of the solution but not a miracle cure.
You can't have real agriculture without manure.
Fossil guano is a finite, scarce and very expensive resource, and human manure is not so desirable as replacement by several reasons so, how do they expect to feed their green miracle exactly?.
How efficient is the conversion food-to-meat is irrelevant if you omit half of the products obtained. This food also will turn into leather, milk, workforce and manure, so the calculus is flawed from the start.