The principle of equal consideration of interests is a very popular principle in animal ethics. Peter Singer employs it to ground equal treatment and solve the problem of the basis of equality, namely the problem of why we should grant equal treatment despite the variability of people’s features. In this paper, I challenge Singer’s argument because ECOI does not provide plausible grounds to presume that the interests of diverse individuals are actually equal. Analyzing the case of pain and the interest (...) in not suffering in particular, I contend that there are some insurmountable epistemic and axiological problems in accounting for the equality of interests. Besides criticizing ECOI as a basis of equality, I argue that we need to rely on an equality of moral status. I conclude by providing some considerations on the relation between equality and the principle of proportionality. (shrink)