The greatest progress in developing objective behavior-based methods of assessing the response to pain and injury has been in farm animals. The following are signs to look for in horses, cattle, sheep and goats, and pigs.
Horses in acute pain generally show a reluctance to be handled. Other responses are varied: periods of restlessness, interrupted feeding with food held in the mouth uneaten, anxious appearance with dilated pupils and glassy eyes, increased respiration and pulse rate with flared nostrils, profuse sweating, and a rigid stance.
Horses in pain also grind their teeth, switch their tails, or play with their water bucket. In prolonged pain, their behavior might change from restlessness to depression with head lowered. In pain associated with skeletal damage, there is reluctance to move; limbs might be held in unusual positions (e.g., stand “parked” with the weight on the hind feet and one front foot “pointed” ahead of the other), and the head and neck in a fixed position.
Horses with abdominal or thoracic pain may look at, bite, or kick their abdomen; get up and lie down frequently; walk in circles; stand “parked” with elbows adducted; and sweat, roll, and injure themselves as a result of these activities, with bruising especially around the eyes.
Cattle in pain often appear dull and depressed, hold their heads low, and show little interest in their surroundings. Their overall activity may be reduced. Other observable changes include inappetence, weight loss, grunting and grindig of teeth, and, in milking cows, decreased milk yield.
Severe pain often results in rapid, shallow respiration. On handling, they may react violently or adopt a rigid posture designed to immobilize the painful region. Localized pain may be associated with persistent licking or kicking at the offending area and, when the pain is severe, bellowing.
Generally, signs of abdominal pain are similar to those in horses, but less marked. Rigid posture can lead to a lack of grooming because of an unwillingness to turn the neck. With acute abdominal conditions, such as intestinal strangulation, cattle adopt a characteristic stance with one hind foot placed directly in front of the other.
Sheep and Goats
Signs of pain in sheep and goats are generally similar to those in cattle, but sheep, in particular, tolerate severe injury without overt signs of pain or distress.
There is a general reluctance to move along with changes in posture, movement and in facial expression. Pain can also cause cessation of rumination, eating, and drinking, and increased curling of the lips; but, as in other species, these are not reliable indicators of pain.
Goats are more likely than cattle to vocalize in response to pain. They may also grind their teeth, have rapid and shallow breathing, change posture frequently, and appear agitated (foot stamping). Dairy goats will quickly decrease production and lose body weight and general body condition. After castration or tail docking, lambs show very characteristic signs of pain by standing and lying repeatedly, wagging their tails, occasionally bleating, and displaying neck extension, dorsal lip curling, kicking, rolling, and hyperventilation.
Pigs in pain might show changes in their overall demeanor, social behavior, gait, and posture and an absence of bed making. They may become apathetic and unwilling to move and may hide in bedding if possible. Pigs normally squeal and attempt to escape when handled, and pain can accentuate these reactions or cause adults to become aggressive. Squealing is also characteristic when painful areas are palpated. More moderate pain may simply reduce activity levels and make the animal less responsive to familiar handlers and reluctant to feed or drink.