it details the events that occur when a sickness sweeps through the Coates family's livestock, including their hogs and cattle. The family tries to keep the animals healthy by feeding them special food and providing them with extra care, but despite their efforts, many of the animals die or become too sick to be saved.
During this difficult time, Old Yeller proves himself to be a valuable member of the family, as he helps to keep the animals contained and even helps to put down some of the ones that are too sick to be saved. Additionally, when Travis and his younger brother, Arliss, contract the sickness themselves, Old Yeller stays by their side and helps to care for them until they recover.
Despite the sadness and hardship of the sickness, Travis notes that it has brought his family closer together, and he reflects on the importance of having a loyal and dependable dog like Old Yeller to rely on in tough times.