There are the obvious causes of pain in animals such as from trauma, post-surgical pain, intervertebral disc disease and arthritis but there are many conditions that cause pain that owners are not aware of.
Remember animals show pain differently to humans and animal species differ in their response to pain. A Labrador can still be wagging its tail even with a deep laceration but it does not mean it is not in pain!
congestive heart failure, pleuritic, thromboembolism ( saddle thrombus in cats), cerebral vascular accident (“stroke” in dogs, cats), pneumonia
Cancer pain: all cancers are painful
Cancers related to the viscera are strongly related to emotional changes in animals.
otitis, severe itching, burns, chronic wounds, abcesses, cellulitis, urine scalding, clipper wounds, severe chin acne, nose inflammation/ulceration, immune mediated disease with blistering
oral tumours, feline oral resorptive lesions ( cavities), tooth fractures, stomatitis, tooth abcess, mouth ulcers
Gastrointestinal: constipation, obstipation, obstruction, megacolon, anal sac impaction, haemorragic gastroenteritis (bloody diarrhoea), pancreatitis, gastric dilation volvulus (GDV), foreign bodies, gastritic, gastric ulcers.
Muscular soreness, arthritis, degenerative joint disease, tendon or ligament injury, intervertebral disc disease, facet pain of spondylosis, fractures, dislocations, sciatica, meningitis, diabetic neuropathy.
corneal disease and ulcers, glaucoma, uveitis
uroliths (bladder and kidney stones), feline lower urinary tract disease, interstitial cystitis, acute renal failure, enlarged kidneys, lower urinary tract infections, urinary obstruction, vaginitis, queening/whelping.
pain associated post surgery. From mild pain associated with a cat castration, moderate pain post bitch spey to severe pain post fracture repair, cruciate surgery and spinal surgery, tail amputations.