Identification of potential physiological and behavioral indicators of postoperative pain in horses after exploratory celiotomy for colic

Abstract

Physiological and behavioral parameters were determined in 27 horses to identify potential indicators of postoperative pain following exploratory celiotomy for colic. Experimental groups were 10 horses that received no treatment (Control), 10 horses anesthetized for a non-painful procedure (Anesthesia), and 7 horses that presented for emergency surgery for acute gastrointestinal disease (Surgery). Physiological and behavioral data were collected on the horses 0, 4, 8, 12, 16, 20, and 24–30 h after entry into a stall in the equine intensive care unit of the Veterinary Teaching Hospital at Washington State University. Physiological data included: heart rate, respiratory rate, and plasma cortisol concentration. For the entire period of observation the surgery group had significantly higher plasma cortisol concentration and significantly elevated heart rate compared to the Control and Anesthesia groups, which did not differ for either variable. A numerical rating scale (NRS) of behavior was used to visually score the horses at the same time physiological data were collected. In addition, time budgets of behavior were calculated from 1 h segments of real-time video recording beginning at the 0, 4, 8 or 12 h, and 20 or 24–30 h time points. Time budgets for the Control and Anesthesia groups did not differ in the time spent in locomotor activities and both groups spent significantly more time in locomotion than the Surgery group. The Surgery group spent significantly more time displaying painful behavior compared to the Control and Anesthesia groups; however, the amount of time the Surgery group displayed painful behavior was small compared to the amount of time with no movement. The NRS scores substantiated the video taped behavioral data with significantly different scores for the Surgery group versus the Control and Anesthesia groups for multi-factor ratings of body posture and response to stimuli. We conclude that reduced locomotion, elevated plasma cortisol concentration, and elevated heart rate are potential indicators of postoperative pain in horses.