Herding animals for both survival and trade has been common practice all over the world for several thousand years. Even today, owning livestock and herding animals is very commonplace, even on the wealthiest portions of the Earth. After disaster, owning animals will give you an enormous advantage to individuals who do not own livestock. Having over 1000 pounds of meat readily available will not only keep you fed and give you an outstanding trade item to sell, it will continue giving. Owning livestock is a lot of work but will pay off in a huge way. If your animals continue to breed, you will have unlimited amounts of readily available, edible meat. This will keep you from having to constantly hunt or barter with traders to buy meat.
The downside is, as said before, a lot of work. Keeping stalls clean, keeping animals clean and making sure they are well fed and watered is no easy task and is best approached with the help of many hands. You also become a valuable target to raiders when you have something so valuable, so security will be extremely important for you if you plan on owning some livestock. You must be near a very large and reliable water source for your animals to survive, so for many people, this will not work due to their location. How ever, for most people, owning a few small animals such as chickens or rabbits is quite easy.
Not only will you get fresh meat when you slaughter these animals, but you will also receive animal hide, which depending on the animal will provide excellent clothing material, in turn being a great trade item. Along with hide, you will receive bone, which can be made into broths and has countless uses. The Native Americans are infamous for using almost every single part of an animal when they kill it for one thing or another. Whether they used bones for armor or bladders for canteens. This approach will also be very useful after disaster. Another down side to owning much livestock is immobility. Having so many animals will make it extremely difficult to move to another location if disaster struck. Even if you are a professional herder, you will be easy picking for desperate individuals looking for an easy score, so beware.
Overall, owning livestock will help you tremendously if you plan on staying in a single location after disaster. Upsides being that you will have access to an enormous amount of fresh meat, natural resources such as hide, bone and antler as well as having a reliable and valuable trade item. Downsides include being almost completely immobile, and needing a lot of water and feed to ensure survival of your animals. Other downsides include being a prime target for raiders and needing to do a lot of manual labor to maintain a functional system of livestock.