The effect of chronic clinical pain on thermal and mechanical thresholds in sheep

Abstract

Threshold responses were measured to a thermal skin test and a mechanical pressure test in two groups of conscious unrestrained sheep. The first group of sheep were healthy adult females and formed a control sample, the second group were also adult females, but were all suffering from a condition known as footrot. Footrot is a chronic infective lesion affecting usually one foot which appears to cause severe pain in its worst manifestation. These sheep were assessed for the severity of the lesion and degree of lameness and were divided into high and low severity subgroups. Footrot did not alter the threshold to the thermal test but the mechanical pressure threshold was significantly reduced in both footrot sub-groups compared to controls. A local anaesthetic block of the affected foot restored values to close to the control level. After treatment of the affected foot, the mechanical threshold in the low severity sub-group was returned to normal, but in the high severity sub-group it was still significantly reduced compared to the control animals. However, when retested 3 months later these values had returned to the normal control levels.

Development of a facial expression scale using footrot and mastitis as models of pain in sheep

“…Footrot was used as our pain model following previous research showing the link between lameness due to footrot and mechanical hyperalgesia (Ley et al, 1989). We followed methods by Langford et al (2010), Sotocinal et al (2011), Leach et al (2012), Keating et al (2012) and Dalla Costa et al (2014) to develop our scale.…”

“…Mechanical threshold responses are also significantly reduced when severe footrot is present, indicating the presence of chronic pain; the application of a local anaesthetic block raises the threshold to be in line with that of healthy sheep (Ley et al, 1989). Resolution of the lesions does not necessarily remove this pain, as hyperalgesia to a mechanical stimulus may still be present for up to three months in sheep that had previously suffered from severe footrot (Dolan et al, 2003;Ley et al, 1989).…”

Behavioural adaptations of sheep to repeated acidosis challenges and effect of yeast supplementation

“…A lower sensitivity to pain based on CO 2 laser measurements has been reported under acute stress (Rushen and Ladewig, 1991), whereas a higher sensitivity to pain has been observed under chronic stress (Gamaro et al, 1998) or chronic pain (Ley et al, 1989). In addition, rumen inflammation is reported during acidosis (Krause and Oetzel, 2006), which could induce an acute phase of inflammatory response.…”

The inter- and intra-observer reliability of a locomotion scoring scale for sheep

“…In sheep, 40 lameness is associated with pain (Ley et al, 1989) with a gold standard (Dawson-Saunders and Trapp, 1994) which assessed the scale's 58 accuracy and objectivity. However, there is no gold standard to assess locomotion.…”