To allow a continuous assessment of pain, VAS uses a 10 cm line labelled at '0' with 'no pain' and '10' with 'worst pain'. The line is marked at a point corresponding to the assessment of the pain. The distance of the mark from zero is measured. This scale has been used to assess castration pain in lambs (Thornton & Waterman 1997; Kent et al 2001b, 2004) and post operative pain in dogs (Holton et al 1998; Firth & Haldane 1999).
Example of a VAS
VAS has also be used to assess the severity of wounds, degree of lameness (Welsh et al 1993), activity levels.
Kent and her colleagues (2004) demonstrated how VAS could be used in a field trial to show that pain resulting from rubber ring castration could be significantly reduced (Results) by the use of local anaesthesia or crushing the nerves to the scrotum and testes.
Videos of the lambs in the validation experiment, were also used to show that experience of assessing pain increased the accuracy with which individuals assess pain using VAS (Results) (Kent et al 2001b).