Analgesic effects of morphine and butorphanol in broiler chickens.

OBJECTIVE: To evaluate analgesic efficacies of morphine and butorphanol in lame broiler chickens. STUDY DESIGN: Double blind, randomized, controlled experimental study. ANIMALS: In study 1, 36 lame and 36 sound chickens. In study 2, 48 lame and 48 sound chickens. METHODS: Sound and lame chickens were gait scored and randomly assigned into four groups: sound-drug, sound-placebo, lame-drug, and lame-placebo in study 1. In study 2, an additional lame and sound handling control group was included. Chickens in drug groups were injected with either morphine or butorphanol 2 mg kg-1 intravenously. Chickens in placebo groups were injected with an equal volume of normal saline. All birds underwent an obstacle course (OC) and latency-to-lie (LTL) test before injection and at 30 minutes and 2 hours after injection, to assess their walking ability and their standing ability. The time taken to finish the OC and the standing time in the LTL test were recorded. Friedman tests with Dunn's correction were used to identify significant differences. RESULTS: Lame chickens finished the OC faster (mean ± standard deviation 36 ± 8 c.f. 69 ± 18 seconds) after the injection of butorphanol. Morphine caused sedation with an increase in time taken to finish the OC, even in sound chickens. In the lame handling control and placebo groups the OC times increased and the LTL times decreased with each observation. CONCLUSION: Intravenous butorphanol (2 mg kg-1) may be analgesic in chickens for up to 2 hours. Morphine caused sedation.

Effect of age at castration on behavioural response to subsequent tail docking in lambs.

OBJECTIVE: To investigate the effects of age at castration on the subsequent behavioural response to tail docking. STUDY DESIGN: Randomised prospective blinded experimental study. ANIMALS: Forty-five male lambs were admitted to the study at birth. METHODS: The lambs were allocated into two groups for castration by rubber ring at 1 (1D, n = 20) or 10 (10D, n = 25) days of age. Following castration both groups of lambs were tail-docked by rubber ring at between 26 and 34 days of age. Their behavioural responses to tail docking were recorded by video for 30 minutes before (n = 11) and 30 minutes after (n = 45) tail docking. Statistical differences were tested using anova with Mann-Whitney post-hoc testing. RESULTS: Two data sets were removed resulting in n = 19 and = 24 at 1D and 10D, respectively. A significant increase in the incidence of active and abnormal postural behaviour was seen in both groups after tail docking. Three behaviours were significantly different (p < 0.05) between the two groups. These behaviours were rolling, standing unsteadily and the total proportion of time standing with abnormal posture. These behaviours all had greater incidence in the lambs castrated at 1D of age. CONCLUSIONS: Lambs castrated at 1D appeared to perceive a greater intensity of pain after subsequent tail docking than lambs castrated at 10D. CLINICAL RELEVANCE: The timing of a single noxious stimulus in young animals can affect subsequent pain perception.

Electroencephalography during ovariohysterectomy in rats anaesthetized with halothane.

OBJECTIVE: To evaluate electroencephalographic (EEG) changes during ovariohysterectomy (OVH) in rats anaesthetized with halothane, and modification of the EEG changes by the co-administration of fentanyl, ketamine or thiopental. STUDY DESIGN: Prospective, randomized, blinded controlled study. ANIMALS: Sixty adult female Sprague-Dawley rats. METHODS: Anaesthesia was induced and maintained with halothane [Fe'HAL 0.95 +/- 0.05%]. The electroencephalogram was recorded continuously from the left and right primary somatosensory cortices. Rats were randomly divided into four groups and a rapid IV infusion of physiological saline, thiopental, ketamine or fentanyl was administered. OVH started 10 minutes after drug administration. Blood samples, for assay of plasma drug concentrations, were collected 5 minutes after administration and at the end of surgery. Electroencephalograph descriptors median frequency (F50), spectral edge frequency 95% (F95) and total power (P(tot)), recorded during non-surgical baseline periods, were compared with those recorded during defined surgical periods; skin incision, right and left ovarian pedicle ligation; cervical ligation. Plasma drug concentrations were measured using high performance lipid chromatography. RESULTS: Although a large number of statistical differences in EEG data were observed, these generally represented a reduction in F50 or F95 throughout the experimental recording period and were similar between groups. A significant reduction in P(tot) occurred during ligation of the ovaries and cervix in the control group compared with other recording periods. The co-administration of ketamine, fentanyl and thiopental obtunded the reduction in P(tot). CONCLUSIONS AND CLINICAL RELEVANCE: Electroencephalographic changes, in the control group, mimicked changes reported in other studies using the minimal anaesthesia model. However, the stability in F50 during the surgical period compared with the baseline period indicated that OVH is an unsuitable surgical stimulus to investigate EEG changes with noxious stimulation. This may be attributed to the relatively prolonged duration of this surgical procedure and the primarily visceral afferent sensory innervation of the genital tract.

Effects of age on the electroencephalographic response to castration in lambs anaesthetized with halothane in oxygen from birth to 6 weeks old.

OBJECTIVES: To characterize changes in the cerebro-cortical response of lambs to rubber-ring castration during the first 6 weeks of postnatal life. ANIMALS: Coopworth-Texel cross ram lambs between 3 hours and 44 days of age. METHODS: The electroencephalogram (EEG) and heart rate responses to rubber ring castration were compared. Anaesthesia was induced via a face mask and maintained with halothane in oxygen (e'(Hal) = 1.2%). Once a stable plane of anaesthesia had been achieved, data collection of EEG and electrocardiogram (ECG) commenced, and the lambs were castrated 15 minutes later, using rubber rings. Heart rate was derived from the ECG and the median frequency (F(50)), spectral edge frequency (F(95)) and total power (p(tot)) were derived from the EEG. RESULTS: Castration-induced changes in F(50) increased from 2 +/- 1.8% in the youngest lambs to a maximum of 33 +/- 8.9% in the 36 +/- 0.5 day-old lambs. Changes in F(95) increased from -7 +/- 3% in the youngest lambs to a maximum of 16 +/- 11% in the 36 +/- 0.5 day-old lambs. Linear regression analysis in lambs up to 10 days of age demonstrated a change in the response with age that was significantly different from zero for F(50) (r(2) = 0.28, p = 0.007) and F(95) (r(2) = 0.38, p = 0.001), but not for p(tot) or heart rate. CONCLUSION: This study identified significant changes in the responsiveness of the lambs' cerebral cortex to the noxious stimulation of castration over the first 7-10 days of postnatal life. The results suggest that mechanisms that suppress responses of the fetus to noxious stimulation may still be active in the first few days after birth. CLINICAL RELEVANCE: This study documents changes in central nociceptive processing which may reflect the ability of neonatal animals to perceive pain.

Is it possible to generate cerebral evoked potentials with a mechanical stimulus from the duodenum in rats?

The study aim was to develop a model to generate cerebral evoked potentials (CEPs) by mechanical distention of the duodenum in rats. Twenty Sprague-Dawley rats were anaesthetized and the EEG recorded from the left and right somatosensory cortices (S1L, S1R). A balloon catheter was implanted into the duodenum. A pneumatic device, triggered by data acquisition software, inflated the balloon for 200 ms every 3s to deliver a repeatable noxious stimulus. EEG was recorded for 100 ms before and 500 ms after onset of inflation and the response to 512 stimuli averaged to generate a CEP. Two CEPs were generated in each animal and data summed to calculate a single CEP for each channel. Data were excluded when the signal to noise ratio was < 2, therefore data are presented from 11 animals. A repeatable CEP was identified in waveforms recorded from S1L. The mean (S.D.) CEP comprised a triphasic waveform (P1, N1, P2) with latencies of 246.0 (24.7), 289.3 (12.8) and 321.5 (13.2)ms, respectively. We are the first group to have generated and characterized a CEP following mechanical stimulation of the duodenum. This model can be applied to further elucidate the mechanisms leading to visceral pain perception.