I'm going to ignore the gene-splicing-to-speed-this-up part as that's simply a Clarkian Magic way of avoiding the 500 year timeline. I'd be surprised if someone could tell you, "oh, yeah, change that gene to get that effect and this gene to get this effect...." We don't understand our own genome to do that. So, let's focus on what you want in your food stock and you can handwave how to get it quickly.
You have two options: stock bred for corrals that maximize the meat but also maximize the cost or stock bred to hunt. Corrals allow you to better control the breeding program, but they're a hassle. Hunting combines sport with food and allows the humans to breed like rabbits, but you basically loose control of the details.
Assuming you want the best possible food source, your goals after 500 years would include...
Supple, somewhat fatty flesh with a high ratio of muscle mass to total mass.
Short hair to minimize care and disease.
Sunburn-resistant skin (I'm assuming outdoor corralling of a lot of stock and a sense of capitalism in that they won't waste resources to clothe the stock).
Docility, stock is expensive and the last thing you want is stock damaging stock. Besides, athletic stock tends to produce tough, stringy meat and we want our long pork to fall off the bone when cooked.
To that end, you might also want to breed for shorter arms (minimizing throwing/swinging leverage) and possibly even stunted hands. No tool building on the range, please.
As an aside, it's worth noting that what you're doing is little or no different than what people in Africa have done for thousands of years with Chimpanzees. Those people didn't have the level of control over chimps that you're suggesting your aliens have over humans, but the problems are basically the same. Chimps are intelligent and have the ability to use local materials as basic tools. Humans, like chimps, can do a lot of damage with a stick.
- After 500 years your humans would lose the art of language, but only if you have some method of forcing them to never talk or write. This is a serious problem for your breeding program. I expect you'll be removing tongues for the first 100-200 years to guarantee no talking. You would also need to do something about scratching words in the dirt. But, if you're breeding those short, stumped arms, that might take care of itself. Language in any form is your enemy. With it, you're holding the proverbial tiger by the ears. Without it, you have dull-eyed cows turning food into fertilizer.
On the other hand, if what you want is volume and a little fun on the side, then you should not only consider the ancient and modern plight of the Chimpanzee, but you should also consider how humans were presented in the original Planet of the Apes film. They couldn't speak or write (too much time had passed). They were docile and afraid of their ape masters once caught. They were hunted for sport (if not eaten). Basically, they're exactly what you want for food stock in the wild, and the greatest benefit is that, unless overhunted, you'll have more of them.
As a final note: you're dealing with a species that is cognitavely capable to a much greater degree than chimpanzees. Humans are not monkeys with the gift of gab. Put into a situation where we have enough time, despite having lost the gift of language, we'll start problem-solving, organizing, and learning. This will always be a point of unbelievability in your story unless accomodated. Any specie capable of language will eventually learn it, one way or the other, unless controlled to so great a degree that it isn't economically worth keeping them as a food source. Breeding humans into "hoof stock" is quite a bit less believable than simply culling people from the popoulation today.
BTW, a lot of stories have been written over the years suggesting how you could turn humans into a food source. I wish I could remember its title, but I remember one where the aliens had been convinced by a collaborator to stop slaughtering the humans and instead cut off pieces of meat for consumption, letting the humans continue to live and breed. The humans eventually overcame the aliens and the monarchy they had set up and cut the collaborator down (litereally) to where all he had left was ears to hear the screams of children. I wonder what came first, that short story or "The Princess Bride"?
