Apple cider vinegar is, well, as the name states. The stuff you need is unpasteurized and has the 'mother' in it, which the label will state in both cases. If the label states neither you may as well not buy it.
Many people use Braggs' but I prefer Melrose of other brands, for some reason Braggs' does not work like it should, in my experience. I expect that since it's imported it was irradiated and thus, regardless of what the label claims about it being unpasteurized, it has effectively been pasteurized. Local is better if you can get it.
In studies it's been proven to permanently elongate the cilia in the digestive system of chickens, so they are both more feed efficient and less prone to some diseases. It improves their ability to digest, in other words, and their general gut function. It's great for cutting through buildups of overprocessed oils or cooked fats which the body's own enzymes struggle to cope with, which is especially important for birds who do not free range and whose sole staple is pellets or crumble.
It's also great for detoxing, especially heavy metals, as the pectin in apples is one of the few things to remove aluminum, which otherwise can accumulate for decades without lessening. Aluminum buildup causes some seriously devastating diseases, which more often descend onto the next generation so healthy looking people can produce only severely damaged offspring which can be traceable back to exposure in the parent's youth to excess aluminum. It's used in Europe to keep drinking water clear, I'm not sure what other countries use it.
AVC also helps alkalize them, so basically lessening the likelihood of acidosis and its many related diseases.
It helps with the cardiovascular system, helping keep capillaries supple and flexible, and helps with removing plaque buildup in arteries. It's very beneficial for the liver as well.
It is also high in potassium, which can help with many things, and if you've ever received radiation exposure it will help with that... But you will feel nauseous as your body processes it.
One way to tamper with genetic transference from parent to offspring is to induce hypokalemia in one parent, but it has many more effects than that, just like any vitamin. Lack of certain vitamins and minerals can effectively phenotypically 'blank' one parent out of the equation so you get what appear to be carbon copy offspring of the one parent with sufficient nutrition.
There is evidence to suggest the AVC in water helps prevent spread of diseases via drinking sources. Some people use ACV to help ferment their grains/seeds for their animals.