Effects of age on the electroencephalographic response to castration in lambs anaesthetised using halothane in oxygen.
OBJECTIVE
To use the electroencephalogram (EEG) to ascertain whether the response of the cerebral cortex to the noxious stimulus of castration varied with age in lambs.


METHODS
Two groups of East Friesian lambs were selected according to age; the mean age of the younger group (n=21) was 12 (SD 2) days and the older group (n=20) was 29 (SD 1) days. Anaesthesia was induced via mask using 4% halothane in oxygen, and maintained using 1.5% halothane in oxygen at a flow rate of 4 L/min. Once a stable plane of anaesthesia had been achieved, data collection of EEG and electrocardiographic (ECG) readings commenced, and the lambs were castrated 15 min later, using rubber rings. Median and 95% spectral edge frequencies (F95) and total EEG power (ptot) were derived from data from the EEG.


RESULTS
Following castration, there was an increase in the median frequency (F50) in the younger lambs (p=0.002), and an increase in ptot in both groups (p=0.05), which was of greater magnitude in the older lambs. There were no significant changes in the F95. Both younger and older lambs exhibited a transient bradycardia (p=0.001 and p=0.01, respectively).


CONCLUSIONS
These differences in the cortical response between the two groups suggest that 2-week-old lambs undergo a qualitatively different perception of the noxious stimulus of castration compared to 4-week-old lambs.
Johnson
C B
CB
Animal Welfare Science and Bioethics Centre, Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Private Bag 11222, Palmerston North, New Zealand. c.b.johnson@massey.ac.nz
Stafford
K J
KJ
Sylvester
S P
SP
Ward
R N
RN
Mitchinson
S
S
Mellor
D J
DJ
D000367:Age Factors; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D001919:Bradycardia / Q000453:epidemiology / Q000662:veterinary; D004562:Electrocardiography / Q000662:veterinary; D004569:Electroencephalography / Q000662:veterinary*; D006221:Halothane / Q000494:pharmacology*; D008297:Male; D009919:Orchiectomy / Q000379:methods / Q000662:veterinary*; D010147:Pain Measurement / Q000379:methods / Q000662:veterinary; D011897:Random Allocation; D012756:Sheep / Q000502:physiology*
D018685:Anesthetics, Inhalation; D006221:Halothane