Changes in appetite, leading to weight loss and dehydration. Excessive sweating or salivation is also a response to painful stimuli. Chronic pain can be more difficult to recognize because the animal becomes more tolerant of the pain and adjusts its behavioral patterns accordingly to minimize the pain. Unless you have evidence to the contrary, assume that a procedure or a condition painful for humans will also be painful for animals. When in doubt, give the animal the benefit of the doubt.
Pain can be considered a potent source of stress, that is a stressor.
It can also be considered a state of stress itself and lead to distress and maladaptive behaviors. Thus, whether pain is considered as a kind of stress or as a stressor depends on the point of reference. Acute Pain is abrupt in onset and relatively short in duration. It can result from an inflammatory process that originated in damaged tissue, traumatic injury, surgery, or exposure to metabolic, bacterial, or viral disease or toxins. Such pain produces a stress response, but usually does not lead to distress, because the pain is short-lived.