> the decline in demand for most meat varieties That doesn't sound right: https://www.google.com/search?q=meat+consumption&hl=en&safe=off&client=firefox-a&hs=

> the decline in demand for most meat varieties That doesn't sound right: https://www.google.com/search?q=meat+consumption&hl=en&safe=off&client=firefox-a&hs=kmi&rls=org.mozilla:en-US:official&tbm=isch&tbo=u&source=univ&sa=X&ei=noNHUYG4FuePiAe_64CIDg&ved=0CDsQsAQ&biw=1280&bih=897 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.