The Importance of who we are exactly Dealing with when Evaluating Utilitarianism

It is important to highlight Posner's discussion and speculation on the domain in utilitarianism. Posner proposes the two following questions:

1) "Whose happiness is to count into designing policies to maximize the greatest happiness?"

2) "Does the happiness of animals count?"

We must take note of who we are exactly talking about and dealing with when analyzing and interpreting utilitarianism. Are we determining utility based on the happiness of humans under the age of 21? Are there other factors in addition to the human population and animals determining levels of happiness today? These are difficult questions to answer.
Nevertheless, I specifically found Posner's use of an excerpt by J.J.C. Smart very interesting. Smart finds it "hard to agree" to the idea that "a contented sheep is as good as a contented philosopher" (52). Yet, he is unable to find evidence in utilitarian theory that separates a happy sheep from a happy philosopher. This allows Posner to conclude, "Since utility in its broad sense is something possessed by many animals, the theory seems to require including sheep and pigs in the population whose happiness is to be maximized"(53). I have personally never thought of utility in economics in such an overly inclusive way. How do animals specifically influence a society's overall happiness in an economic sense? The point Posner attempts to get across is that we must use the "broadest possible conception of the relevant population" (53). While I do agree with Posner that it is important to have a wide-ranging domain, I believe there is a certain extent to how broad the domain should be.