In the book Of Mice and Men, what does the boss use Crooks for on the ranch?

Of Mice and Men was written in 1937. In those days the big growers did not have the kinds of agricultural equipment that have since been developed. The wagons used for harvesting were pulled by big teams of horses or mules. The boss needed a "stable buck" to look after the horses and their gear. He gave the job to Crooks because Crooks was black and had to take any kind of work he could get in those days of undisguised racial discrimination. Crooks probably gets lower wages than the other men. He is at the bottom of the social hierarchy. We can speculate that his injury took place after he took the job, and that it was while he was working with the horses that he got kicked by one of them. He managed to hang onto his job because he was already there and already competent at it. He could not have gotten hired in his present condition. He knows he is "on borrowed time." Sooner or later the boss will fire him and get a younger, stronger man to take his place.