Chute scoring as a potential method for assessing individual differences in arousal among ewes

Abstract

Chute scoring has been used among beef and dairy operations as a method to gauge the relative phenotypic characteristics of animals based on response to physical restraint. While elements of the cattle chute score, such as tail flicking, exit speed, and side kicking, have been validated as behavioral indicators of arousal in cattle, a robust and species-appropriate scale has not been developed for sheep. Given that individual monitoring of breeding ewes is growing in the sheep industry, it could be beneficial to develop such a rating system for ewes. The objectives of this study were to (1) evaluate the consistency of chute score values and behavioral measures over repeated trials, (2) provide a subjective scoring system that human observers may use to identify behavioral indicators of arousal in sheep, and (3) determine if there are physiological measurements which are related to subjective chute scores. Twenty-eight multiparous, crossbred ewes from the same breeding group were restrained in a squeeze chute for 10 min, once a week for five weeks. Trained researchers gave each ewe a chute score based on the behaviors observed. A ‘1−3’ subjective scale adapted from cattle literature was used to designate score values to each ewe (with scores increasing relative to observable agitation). Measures of heart rate, respiration rate, and surface eye temperature were collected while ewes were restrained. Video data of restrained ewes were coded for order of entry, step and bleat rate, and, latency to exit the chute. Chute scores were highly consistent within ewes between nearly all trial day combinations. Positive and significant correlations (Kendall’s Tau) were found between the third, fourth and fifth trials for bleat rate (P < 0.001), step rate (P < 0.001), latency to exit chute (P < 0.001), eye temperature (P < 0.01), and heart rate (P = 0.01). Step rate was a consistent and significant predictor of chute scores on the ‘1−3’ scale (P < 0.0001). Significant differences in heart rate and eye temperature were found between scores 1 and 2, however no overall differences were found between scores 2 and 3 when physiological measures were analyzed independently. Once physiological information was aggregated into a collective arousal response, significant differences were identified between scores 1 and 2 (P = 0.001), and, 2 and 3 (P = 0.05). The authors suggest a simple 3-point scale may be reasonable for detecting relative differences in reactivity for production ewes, with inclusion of elements of active behaviors related to arousal (e.g. vigilance behavior, ear postures).