Maturity: Travis learns a great deal about himself and about life during the course of the novel. He learns that it is important to be responsible, to be brave, and to make difficult decisions. He also learns that life is full of both joy and sorrow, and that it is important to appreciate the good times while they last.
Love and family: The novel also explores the themes of love and family. The Coulters are a close-knit family, and they love and support each other unconditionally. They also learn to love Old Yeller, and he becomes an important part of their family.
Sacrifice: Old Yeller is ultimately willing to sacrifice his own life to protect Travis. This act of sacrifice is a powerful symbol of the love and loyalty that Old Yeller has for his family.
Courage: Travis shows courage in many ways throughout the novel. He faces his fears and does what he knows is right, even when it is difficult. He also shows courage when he makes the decision to put Old Yeller down, even though it is a very difficult decision for him to make.
Responsibility: Travis learns that it is important to be responsible for your actions. He learns that he must take responsibility for his own mistakes, and he must also take responsibility for the care of his family and his dog.
Death: The novel also explores the theme of death. Old Yeller dies at the end of the novel, and his death is a sad event for the Coulter family. However, they also learn that death is a part of life, and they must learn to live with their grief and move on.