[alwaysinshade]

> the decline in demand for most meat varieties

That doesn't sound right:

https://www.google.com/search?q=meat+consumption&hl=en&#...

If anything, where there's been a slight reduction in one area of consumption (e.g. beef) there's been an increase in another (poultry) with an overall rise in meat consumption.

> economics do not allow those animals to be part of the cycle anymore

Given the incredible size of modern farms, using animals as a source of fertilizer is no longer practical. Meat consumption isn't really part of the equation - livestock require food themselves, so you'd need to grow huge sums just to feed the animals as well as produce enough grain/vegetables for human consumption. If you can artificially produce fertilizer then you remove this bottleneck.

Smaller farms would allow animals to be part of the rotation.