Startle magnitude is a repeatable measure of reactive temperament in sheep

Abstract

Behavioural reactivity is an expression of temperament that may influence an animal’s response to stressful situations and impact on handleability and the human-animal relationship. Shortcomings of previously described tests led to the development of a standardized startle protocol in sheep using a tactile stimulus (airblast to the face) and the presence of conspecifics to minimize the effects of social isolation. Here we tested the repeatability of the protocol, the consistency of the response and habituation to the protocol. Twenty sheep were tested across four startle interval test phases. Phases were applied consecutively such that each sheep received up to 17 startles across a six-week period with two to six days between test phases. Phases were; within – up to 5 startles over a 7 min test, Bi-hourly – four repetitions of a single 4-minute startle test 2 hours apart on one day, daily – a single 4-minute startle test repeated over four consecutive days and, weekly – a single 4-minute startle test repeated once per week over four consecutive weeks. Three measures of startle magnitude, retreat distance (zone 1–6) and startle duration (s), startle force (gs), were recorded for each startle. A reduction in response to the startle stimulus over time was identified; however, consistent responses of sheep for the measures of startle magnitude were generally observed across test phases. Repeatability of retreat distance and startle force were moderate to high within test phases (0.56–0.82), whereas startle duration had low to moderate repeatability (0.26–0.50). Strong consistency in individual responses, good repeatability, and the presence of a distinct startle response after repeated applications of the stimulus indicate that the startle test shows promise as a measure of reactive temperament in sheep. Further development to improve the tests access in commercial environments may also facilitate producers use of startle magnitude for the selection of less reactive temperaments to improve handleability, safety and welfare on farm.