Well, I confess I don't know the actual numbers. But most places on Earth don't have the intensive farming found in the Americas.
> Aren't we just talking about the inefficiency of raising animals as a food source?
Quite the contrary. In a sibling comment I discuss how ruminants are the most efficient way to turn inedible plant matter to food that humans can eat.
The wikipedia page on "ruminant" has some interesting information about the process of rumination. In short, ruminants have four stomachs. In the first two, plant matter is fermented by bacteria, then regurgitated so that it can be re-chewed to hydrate it with saliva, that promotes bacterial development and controls the pH of these stomachs. The third stomach is a kind of filter that absorbs some nutrients and allows only food of certain size to pass to the final, fourth stomach. The fourth stomach is the true stomach that is similar to the one we have in our beliies. So to eat the plants that ruminants are specialised to eat, we'd need to have it first chewed and pre-digested by ruminants. In yet another comment I noted how sheep and cows that range freely eat wild grasses, and goats eat shrub.
As I say in that other comment, factory farmed cows are fed soy and corn, that humans can also eat, rather than wild grasses that humans can't eat. But that is factory farming. It is actually harmful for ruminants to feed them that kind of food and so it's a practice that should absolutely be eliminated, along with the rest of factory farming.
Far as I can tell, nobody has been able to breed goats in factory farms. And sheep are normally not factory farmed. I don't know what it is that makes cows good for that sort of thing, but you can be assured that where farming is primarily of sheep and goats, whatever automation of processes there exists is nowhere near the scale of factory farms with giant, thousand-animal feedlots as in the Americas.
Anyway I think "efficiency" is a red herring. The farming industry is very efficient at producing cheap meat by the thousand-ton. But human bodies are not tuned to a world were food is produced "efficiently". We are predisposed to eat as much as we can as soon as we can, to make up for the difficulty of finding enough nutrients to sustain us "in the wild". Presented with the extravagant amounts of cheap meat produced by industrial farming, we are inevitably drawn to excesses of consumption. These excesses are used by the very industry that caused them in the first place as justification to produce even more meat, throwing even more fuel to the fire, destroying even more of the environment and treating even more hundreds of thousands of animals like garbage. Inevitably, there is a backlash and people swear off meat, when what we should all be swearing at and off is the meat industry, that would happily farm us if it was profitable.