Response or Comment
While the primary goal of the animal welfare movement is to eliminate suffering in those animal species that are exploited by humans, this goal, although exemplary, is narrow sighted. Notwithstanding the practical difficulties of proving animal suffering, especially psychological, suffering could conceivably be eliminated, as in confined farm animals, through the use of tranquilizers, or even brain surgery. A goose being made to eat compulsively, following selective partial destruction or stimulation of its brain to cause hypertrophy of its liver for the liver pate trade, may not suffer. But it is being harmed. Likewise, to selective breed a farm animal, like a broiler chicken, that eats to excess and its rate of growth jeopardizes its health, or to raise a zoo or laboratory animal in a highly restricted environment, may not cause overt suffering, since the animals do "adapt." But they are being harmed, since such treatments can increase their susceptibility to stress and disease. In the parlance of animal rights philosophy, their rights are being violated, regardless of whether or not suffering occurs or can be scientifically proven.
Fox, M.W. (1983). Humane ethics and animal rights. International Journal for the Study of Animal Problems, 4(4), 286-289.