Why are Jody's dad and Billy Buck going to Salinas in Steinbeck's "The Gift"?

Billy Buck and Jody's father leave early in the morning with older dairy cows that they are taking to the butcher. As they depart on horseback, Jody sees them

...drive six old milk cows out of the corral and start over the hill toward Salinas. They were going to sell the old cows to the butcher.

The two men turn the trip into more than a delivery because when they return home in the darkness of evening, Jody knows that they enjoyed some leisure activities before departing. At supper his father tells Jody that he better get to sleep because he is going to need him in the morning. Of course, Jody wonders what is going to occur the next day. As he lies in bed, trying to hear his parents as they talk downstairs, the boy cannot detect many words said beneath him. However, he hears his father tell his mother, “But, Ruth, I didn’t give much for him.” So, Jody knows that some animal has been purchased.
In the morning Jody dresses hurriedly, eats quickly, and eagerly anticipates what he will see as he follows respectfully behind the two men who head to the barn. Because it is darker in the barn than outside, Jody's eyes must adjust to the dim light. Soon, however, he can make out a red colt in the stall. "Jody’s throat collapsed in on itself and cut his breath short" because of his excitement. His father tells Jody to take good care of him or he will sell the colt. Every day Jody devotes time to his prized gift.
Tragically, though, Jody's little horse dies after becoming too cold in a winter rain and then running out one night when he is not yet well. This experience teaches Jody about death, and he passes from innocence to experience.