Spot is the ill-tempered spotted milk cow belonging to Travis and his family. Rose was the family's old brown cow, but she was unreliable when it came to milking. Her calf, Spot, turned out to be much more productive. The reader is first introduced to Spot in chapter 7.
The main problem with Spot is that she has the habit of wandering off on her own. She does not like to stay with the other cattle and frequently hides in the brush. She also does not care for being handled by Travis or anyone else. As Travis says, "Spot didn't want to be friends with anybody."
However, Spot is a dutiful and protective mother. When Travis finds Spot just after the cow has given birth, she chases the boy away with the intent of really hurting him. It seems that Old Yeller is the only one who can really handle this grumpy bovine. The dog figured out that if he can bite down and hold on to Spot's nose, he can drive her onto her back. After that happens, the cow seems to have developed a healthy fear of the dog and will go where she is driven if Old Yeller is there. Even when it comes to milking, Spot will only tolerate the activity if Old Yeller is there to keep her in line.
Sadly, Spot meets a bad end. In chapter 13, she is the first animal on the ranch to contract hydrophobia (rabies). Sadly, Travis is forced to kill the poor sick cow in the following chapter.