Graph comparing the plasma cortisol response in 3 to 4 month old calves scoop dehorned with and without local anaesthetic.
The peak plasma cortisol (- 135nmol/l recorded as changes from baseline values) occurs within 30 minutes of treatment after scoop dehorning and there is a secondary peak of 50 - 60 nmol/l above baseline between 1 and 6 hours after treatment. These two cortisol peaks are abolished between treatment and 5 hours post treatment by the use of local anaesthetic. However, a cortisol response peaking at 130 nmol/l occurs 6 to 8 hours after treatment, suggesting that using local anaesthetic with this method of dehorning only delays the cortisol, and by inference the pain.
The graph below shows that a delayed peak does not occur when local anaesthetic is used with hot iron dehorning of six week old calves (Petrie et al 1996).
Graph showing the cortisol response in six week old calves dehorned with a hot iron, with and without local anaesthetic use.
DH - Hot-iron dehorning without anaesthetic
DHLA - Hot-iron dehorning with local anaesthetic
sham - Handled control calves
Hot iron dehorning of six week old calves results in a peak plasma cortisol value 47 nmol/l above baseline values within 30 minutes of treatment with values remaining about 10 to 15 nmol/l above baseline values from 1.5 to 9.5 hours after treatment. Use of local anaesthetic with this method of dehorning gave a peak cortisol response of about 22 nmol/l with values remaining between 5 and 20 nmol/ l between 1 and 9.5 hours after treatment. There is no delayed cortisol peak as seen after scoop dehorning. The cautery appears to destroy the nerve endings, reducing nerve impulses from the area, as well as reducing any haemorrhage.