How can we tell that Willie's grandfather knew about the horses?

Willy's grandfather easily guessed Beauty's age, ordered him a special diet, and paid close attention to his legs. He knew his horses.

The farmer slowly felt my legs, which were much swelled and strained; then he looked at my mouth. “Thirteen or fourteen, I should say; just trot him out, will you?” illie's grandfather easily guessed Beauty's age and took special care to give him the proper diet and care for his ailing legs.

There was not a day when he did not pay me a visit; sometimes picking me out from among the other horses, and giving me a bit of carrot, or something good, or sometimes standing by me while I ate my oats. He always came with kind words and caresses, and of course I grew very fond of him. He called me Old Crony, as I used to come to him in the field and follow him about. Sometimes he brought his grandfather, who always looked closely at my legs.