Effects of mirror-image exposure on heart rate and movement of isolated heifers

Characteristics of a fear response in cattle include an elevated heart rate , and behavioural signs of agitation. Cattle exhibit this response when vis ually isolated from herdmates. Two trials were conducted to determine wheth er exposure to a mirror reduces the stress of social isolation of heifers c onfined within a weigh scale (Trial 1, n = 41), and whether the response di ffers with a frontal or side-view of their mirror-image (Trial 2, n = 38). Crossbred beef heifers (383.3 +/- 3.9 kg) were exposed to their designated treatments for 1 min each day for 10 and 5 consecutive days in Trials 1 and 2, respectively. During the exposure, heifers were confined in social isol ation on a single-animal electronic scale. Remote telemetry was used to rec ord heart rate in beats per minute (HR). The behavioural response (the amou nt of movement) was quantified by an electronic movement-measuring-device ( MMD). The MMD monitors changes in voltage from the load cells of the electr onic scale and records a peak when a trend in voltage is reversed. The grea ter the number of peaks the more the animal moved during exposure. Heifers exposed to a side-view mirror in Trial 1 had overall lower average HR compa red to the no-mirror group (91.5 +/- 1.4 and 98.5 +/- 13 bpm, respectively; P < 0.05), while the amount of movement recorded was no different. Heifers exposed to a front-view mirror-image in Trial 2 had an overall lower avera ge HR compared to the side-view mirror group (91.9 +/- 1.9 and 98.0 +/- 2.0 bpm, respectively; P < 0.05). The front-view group also displayed less mov ement compared to the side-view group (34.8 +/- 4.1 and 68.9 +/- 6.6 MMD pe aks, respectively; P < 0.01). In both trials heifers habituated to the trea tments (had lower HR and less movement) as the days of the trial advanced. The mirror-image did reduce the response to isolation, but had a greater ca lming effect when viewed directly in front of the animal. The reflected sid e-view may simulate the threat posture of an unfamiliar animal more so than a frontal view and therefore be less effective at reducing isolation stres s. (C) 1999 Elsevier Science B.V. All rights reserved.