it would make most sense to use plants that are not considered edible for humans but that are used for tropical livestock feed - of which there are many
Theoretically, if the Human food is productive enough (and nutritious enough for all parties involved), it makes more sense to plant them twice (for humans and animals), and so any excess produced in either area could feed the other (and it seems to me it could go both ways). In contrast, feed can be used ONLY for livestock, and any excess can't be fed back to humans. Additionally, almost all non-human based livestock forage is grazer food, which is useful for pasture-raised pigs but they're not designed for such a strict diet; they need a little more nutritional oomph than mere grass and legume forage can provide. Food for pigs (like non-forage commercial cattle diets) are usually based on some variant of human food anyway, be it grain, starch crops, vegetables or what have you, so weather the plants grown are more useful for humans is a moot point for pigs, since they eat the same stuff, not the graze forage.
*Note: I have been contemplating the Babirusa, which is better adapted for a Grazer/Browser diet and is amenable to domestication, but that's another tangent altogether; besides, there's no guarantee I could get them, but pigs are readily available.
There are people all over the world, and in every corner of the world, who are malnourished or starving, and having an overabundance of food in some areas, it does not make sense to feed that to livestock, who are themselves far less sustainable than plants are... Surplus produce can be used for sale at fair prices and can easily solve the world's hunger problem. Feeding such food to pigs, which would eat plenty of foods that are not palatable to humans and are cheap and easy to produce, is an insult to the starving. It's also wasted opportunity for modest profits, that would otherwise go down the hole of expensive and unnecessary livestock.
Bold: Livestock is not more nor less sustainable than plants are. That's not an issue inherent to the livestock itself, but to the practices under which they're currently raised. Western diets include too much meat, but we don't have to throw out the baby with the bathwater by giving up meat altogether. They're not unnecessary; I wouldn't consider meat, eggs and dairy to be absolutely vital, but it can be sustainably raised and be a good nutritious element of a complete diet.
Not-bold: That's not a food production problem, that's a food distribution problem, as even without my contribution there's more than enough food worldwide to feed the starving right now, but Big Business isn't having any of it. Also, it's an "Either/Or Fallacy" or false dichotomy: I don't have to choose between humans and livestock, both can be done without taking from the other; there is enough, and it should be distributed.
Also, "an insult to the starving"?
That was uncalled for. Please, be civil.
The model of using livestock on a large scale for food is in and of itself unsustainable and inefficient, and totally unnecessary as there are so many plants that grow in the tropics that provide complete protein of high quality and amount, that are drought-resistant and fairly disease-resistant and very cheap to produce (moringa of course being one of these). One might prefer to keep a small number of livestock purely for the variety and enjoyment of flavors, but they are easily sustained on foods that humans do not eat - in some cases, plants that can also provide a medicinal value to humans when needed. Keeping more than just a handful of animals on a farm doesn't actually serve any purpose, and risks contaminating and damaging food crops.
Bold 1: I agree, which is why I dislike and reject industrial models of most kinds of agriculture, but just because a farm is big doesn't mean it has to adhere to industrial principles; people focus so much on producing huge amounts on little land that they don't realize how damaging such intensive efforts can be. A more modest amount across a wider swathe of land is much more sustainable (even if not as productive), especially when you're dealing with diversity (which can help the local wildlife, if you don't object to small losses).
Unbold: I don't object to those plants. But again, it's an "Either/Or Fallacy"; you don't have to get rid of one to use the other, you don't have to see the value of one as being a replacement to the other, and just because it's an alternative doesn't mean it's an improvement (I consider both on equal terms). For the second point, see my first reply of this post.
Bold 2: I don't intend to keep huge amounts of livestock, but my primary desire is self reliance (to an extent), and I can't keep a closed reproductive herd of a few animals without suffering inbreeding depression. If I'm going to keep a closed herd (and I'd like to, to maintain my breed standards and be self-reliant in that respect), I need enough animals to account for genetic diversity (not sure how many that is, but I'd go with the minimum). Besides, I don't intend to keep many animals in a small space. If I were to undertake this project, I'd like a vast area where each animal can be comfortable and have more contribution than impact on the surrounding environment. And I wouldn't be dealing with industrial quantities (despite the needed genetic diversity), I'd like to operate on small artisanal farm type principals. The large scale (I.e. population size) is to prevent inbreeding depression, but I wouldn't be operating the commercial/productive aspects of the farm on large-scale principles. It's nowhere near as productive nor efficient as industrial farms, but if I can minimize the impact on the environment (or contribute positively to it outright) and gain a simple steady paycheck, then I'm satisfied. Besides, it would be a diversified farm anyway, so not every crop there would be destined for the pigs. And if properly managed (rotation, etc), Pigs don't have to hurt your crops, nor do they have to hurt the soil.
Many acacias, for example, provide protein for livestock but are not great sources of food for humans. Leucaena leucocephala is another one that grows like an invasive weed, but can be used for livestock fodder (and also has some medicinal value). It can also be used as supports and shade for fruit plants. http://www.tropicalforages.info/key/Forages/Media/Html/Leucaena_leucocephala.htm
Many sources of fruit for humans are not really of high value nutritionally to livestock. Here is a list of tropical feeds and their level of value: http://www.fao.org/docrep/003/t0632e/t0632e04.htm
And also this: https://vslp.org/ssafeed/
I was planning on growing Wattleseed anyway, but I digress. Leucaena leucocephala is very mildly toxic to animals despite its use as a forage, and over here it's a very nasty weed. I wouldn't willingly grow it when I'm trying to eradicate it off my current land. Some weediness is good for some crops, as far as I'm concerned, but it's a case by case basis and Leucaena does not pass muster for me. It has spread all over the south of the island, and I'm pretty sure its environmental impact hasn't been fully positive. And it sinks a very deep taproot. As for the rest, see my first reply of the post; too much emphasis on ruminant forage (it even mentions that it's for ruminants on the page you provided), when I'm talking about pigs, which do share dietary features in common with humans. I don't have much doubt in the way of ruminants, and given their irrelevance to a fruit forum I decided not to mention them here. Since Pigs theoretically might be fed on fruits (which, being an alternative use for them, is relevant here), I focused my topic on them.
Here is also a list of tropical plants for rabbit livestock: http://www.cuniculture.info/Docs/Elevage/Figur-Tropic/chapitre3/plantes-00-Composition.htm
I don't think I intend to deal with Rabbits, but thanks for the info.
Here's a list of plants poisonous to livestock: http://poisonousplants.ansci.cornell.edu/
Some of those are only facultatively toxic (Sorghum is well-known as fodder) or otherwise toxic to humans too; not much for my own list of crops.
If the goal is to be sustainable, there are better ways to do it than to feed perfectly good human food to livestock.
From a practical perspective or otherwise, I disagree. See above on the "Either/Or Fallacy" and the practical parts of my reply. If human food is productive enough, then it's good enough for both; it can still be sustainable. It's not a designated amount, if there's not enough for both, you grow more for both (taking care not to encroach on the environment, instead integrating the environment to the farm in a positive way).
*Edit: I think we've gone way off-topic here.
