Nonhuman primates show remarkably little reaction to surgical
procedures or to injury, especially in the presence of humans, and might look
well until they are gravely ill or in severe pain. Viewing an animal from a
distance or by video can aid in detecting subtle clinical changes. Loud and
persistent vocalization is an occasional but unreliable expression of pain as it is
more likely to signify alarm or anger. Therefore, it should be recognized that a
nonhuman primate that appears sick is likely to be critically ill and might
require rapid attention.
A nonhuman primate in pain has a general appearance of misery and
dejection. It might huddle in a crouched posture with its arms across its chest
and its head forward with a "sad" facial expression or a grimace and glassy
eyes. It might moan or scream, avoid its companions, and stop grooming. A
monkey in pain can also attract altered attention from its cagemates varying
from a lack of social grooming to attack. The animal may show acute
abdominal pain through facial contortions, clenching of teeth, restlessness, and
shaking accompanied by grunts and moans. Head pain may be manifest by
head pressing against the enclosure surface. Self-directed injurious behavior
may be a sign of more intense pain. Primates in pain usually refuse food and
water. If an animal is well socialized (e.g., trained to perform tasks as part of
a research protocol), changes in response to familiar personnel or in willingness
to cooperate may indicate pain.
