Graph showing the effect of using Xylazine and its reversing agent Tolazoline on the plasma cortisol response to scoop dehorning in calves
All cortisol values quoted below are rises above baseline values.
Xylazine did not appear to have any pain relieving effect in this experiment.
Scoop dehorning of these calves, without analgesic treatment, resulted in a mean primary cortisol peak of 78nmol/l, 30 to 60 minutes after treatment, with a secondary peak 40 to 45 nmol/l, 1.5 to 4 hours later.
Use of Xylazine on its own or in combination with its reversing agent, Tolazoline, in handled control calves result in a peak cortisol response between 30 and 90 nmol/l within 60 minutes of being injected (data not shown). This suggests that the these drugs have a stress effect in calves that is probably not related to pain. This effect probably accounts for the first cortisol peak (45 nmol/l) seen when Xylazine is used to sedate scoop dehorned calves. Xylazine also failed to prevent the delayed plasma cortisol peak (50nmol/l) seen 3 to 6 hours after scoop dehorning with local anaesthetic (see graph under local anaesthetics). Use of Tolazoline further increased both the primary (100nmol/l; 30 minutes after dehorning) and secondary cortisol responses (90 nmol/l; 2.5 to 6 hours after dehorning), but not necessarily the pain.
To separate the stress response, probably due to the sedation, from pain resulting from the procedure, other parameters for assessing pain e.g. behaviour need to be correlated with the changes in plasma cortisol values.