Industrial agriculture keeps animals in a stressful environment. When a corporation raising livestock wants maximum return on their investment, they pour more concrete. You want as many animals on that concrete as possible. It’s not natural for an animal to be in those tightly confined quarters known as Concentrated Animal Feeding Operations. As a result they’re subject to disease due to stress and the environment they’re in. And that disease is contagious, so they feed subtherapeutic antibiotics to keep these animals from getting sick, but these also have the effect of increasing performance and weight gain, so it’s a crutch for them.