Good question ...

... Roger Scruton wonders: Should animals suffer?

For Aristotle, Aquinas, Kant and the other great philosophers of ethics, this distinction is not only absolute but foundational to our understanding of the moral life. If you say nothing about it, and give no indication what it means to us humans, that we alone in the world are beset by moral burdens, that we alone are free, responsible and accountable, that we alone are sovereign over our lives and bound by obligations, then you are not likely to say anything plausible about the grounds of moral judgement, or about the absolute principles that govern us. Still less are you likely to cast any light on our relation to the animals, who cannot reciprocate our moral concern, who have no conception of the injustice of their sufferings and who make no claims of their own.