Suffering, by its nature, is awful, and so one needs an excellent reason to cause it. Occasionally, one will have such a reason. Surgery may cause a human being severe postoperatory pain, but the surgeon may be right to operate if that’s the only way to save the patient.
And what if the sufferer is not a human, but an animal? This doesn’t matter. The underlying principle is that suffering is bad because of what it’s like for the sufferer. Whether the sufferer is a person or a pig or a chicken is irrelevant, just as it’s irrelevant whether the sufferer is white or black or brown. The question is merely how awful the suffering is to the individual.
Stuart Rachels, ‘Vegetarianism’, in T. L. Beauchamp & R. G. Frey (eds.), The Oxford Handbook of Animal Ethics, Oxford, 2012, pp. 883-884