355px-Bighorner concept
Bighorners are large mutated bighorn sheep that roam the Mojave Desert. They are dedicated herbivores and are primarily found in wild herds across the waste. Many settlers use them for their horns, meat, and hides. They are generally "laid-back" beasts with surprisingly docile dispositions, in spite of being quite capable of being extremely dangerous when provoked. Do not, repeat, DO NOT get close to Bighorner calves this will provoke the rest of the herd to attack you until you are dead. They have one disadvantage when compared to Brahmin: they can't be used as pack animals, as they just lie down until the burden is taken off.

If you and a couple of your mates can bring one of these down, then you'll be fed for a good number of weeks. Just be sure to keep the meat inside, and drag the rest of the corpse away from the herd, or predators will kill everything nearby when they find it.