Those animals will peak at about eight to ten years; they'll peak in those years, and then they go up and they go down. When they peak you grow them out and put them to the hunt farm.
It's equivalent to a dairy cow, a Holstein cow: when her milk production starts to go down, you market her. When you sell her to the slaughtering plant, whatever dollar she brings is 100% profit, because she doesn't owe you anything. A hunt operates the same way.