Jon's father is such a dyed-in-the-wool hayseed that he can only think of women as breeding stock, and on top of that, absurdly evaluates them using livestock-judging criteria. That's solid enough, but elevating the primary gag is Jon's bored here-we-go-again response. In panel 2, he suddenly remembers his father is insane. His expression in the remaining panels is that of a man disappointed: with his father, and with himself, for thinking for those fleeting seconds that this conversation could be normal. He was calling his father for approval, because he has finally achieved modest success in a basic area of human life, and all he got was a white slavery joke.
Garfield, too, lets us know he understands the joke of the senior Arbuckle's questions. But since he has no vested interest in Jon's dad's reaction, Garfield instead responds to Jon's weary disgust. And it makes him happy. These things matter to cats.