Evaluation of Electroencephalography, Behaviour and Eye Temperature in Response to Surgical Castration in Sheep.

Castration has been demonstrated to cause pain in sheep. However, it is routinely performed for management purposes. Electroencephalography (EEG) has been used successfully to measure pain in lambs in response to castration and other husbandry procedures in livestock. The aim of this study was to evaluate the use of EEG as a measure of pain and analgesia in conscious lambs undergoing castration on farm over a 24 h period. EEG responses were compared to behavioural observations and changes in ocular temperature via infrared thermography. Twenty-four merino ram lambs (18.63 ± 2.06 kg) were used in this study. Lambs were randomly allocated to one of the following treatment groups: (1) castration with pre-surgical administration of meloxicam (0.5 mg/kg Metacam 20 mg/mL injected subcutaneously into the skin of the neck 15 min prior to recording) and lignocaine (applied via intra-testicular injection five minutes prior to castration, 2 mL lignocaine hydrochloride 20 mg/mL, Troy/Ilium) (CML, n = 8); (2) castration only (C, n = 8); (3) sham castration, handling only (SC, n = 8). EEG was recorded for 5 mins pre-procedure (prior to any intervention), and for 5 mins post-procedure at 0, 1, 4 and 24 h. Behavioural reactions to the procedure were scored, and behaviours were scan sampled at 5 min intervals at the above time points, by blinded observers. Eye temperature was measured for five-minute intervals at each time point. EEG decreased from baseline to 0 h for CML and C groups (p < 0.001), C group values returned similar to baseline at 24 h. Eye temperature increased post-castration at 0 h for C group, no initial change was seen for CML or SC groups. CML and C groups were more likely to have higher reaction scores and showed more abnormal behaviours (p = 0.017). CML and C groups had similar results, indicating minimal effect of analgesic intervention. Lambs in SC group showed significant EEG changes, suggesting that stress from handling also impacted EEG results.

Erratum: Harris, C.; White, P.J.; Mohler, V.L.; Lomax, S. Electroencephalography Can Distinguish between Pain and Anaesthetic Intervention in Conscious Lambs Undergoing Castration. Animals 2020, 10, 428.

The authors wish to make the following corrections to this paper [...].

Electroencephalography Can Distinguish between Pain and Anaesthetic Intervention in Conscious Lambs Undergoing Castration.

Australian sheep routinely undergo painful surgical husbandry procedures without anaesthesia or analgesia. Electroencephalography (EEG) has been shown to be a successful measure of pain in livestock under a general anaesthetic. The aim of this study was to compare this EEG model to that of conscious lambs undergoing castration with and without local anaesthesia. Sixteen merino crossbred ram lambs 6 to 8 weeks of age (13.81kg ± 1.97) were used in the study. Lambs were randomly allocated to 1 of 4 treatment groups: (1) Conscious EEG and surgical castration with no anaesthetic intervention (CON; n = 4); (2) Conscious EEG and surgical castration with pre-operative applied intra-testicular lignocaine injection (CON + LIG; n = 4); (3) surgical castration under minimal anaesthesia (MAM; n = 4); (4) and surgical castration with pre-operative lignocaine injection (2 mL lignocaine hydrochloride 20 mg/mL, under minimal anaesthesia (MAM + LIG; n = 4). Distinct differences in the EEG parameters Ptot, F50 and F95 between pre-and post-castration in conscious lambs were demonstrated in this study (p < 0.01). Further, CON and CON + LIG treatments were distinguishable using F50 and F95 measures (p = 0.02, p = 0.04, respectively). Significant changes in the EEG output of MAM animals were identified pre- to post-castration (p < 0.01). The EEG output of MAM and MAM + LIG were similar. EEG was successful in differentiating lambs treated with pain relief in a conscious state after castration by examining F50 and F95, which may suggest the suitability of conscious EEG pain measurement.

Topical anaesthesia reduces sensitivity of castration wounds in neonatal piglets.

The aim of this study was to do determine the efficacy of the topical anaesthetic Tri-Solfen® in the amelioration of the pain of castration in piglets. The trial was conducted over a three day period, and blocked across six litters with 12 piglets treated on days one and two, and 16 on day three. The piglets were randomly allocated by weight and litter to 1 of 4 treatment groups: (i) sham castration (SHAM; n = 10); (ii) surgical castration with no anaesthetic intervention (CAST; n = 10); (iii) surgical castration with post-operative topical anaesthesia (TRI; n = 10); (iv) surgical castration with a pre-operative intra-testicular lignocaine hydrochloride injection (LIG; n = 10). Wound sensitivity testing involved von Frey monofilaments of weights 4g and 300g, and an 18 gauge needle, used to stimulate the wound and surrounding skin respectively, at various pre-determined sites. Neonatal piglets receiving topical anaesthesia (Tri-Solfen®) spray into castration wounds had significantly lower wound sensitivity responses for up to 4h, compared to those castrated following intra-testicular lignocaine injection or those with no treatment. The use of topical anaesthetic is suggested as a practical and affordable method of improving piglet welfare during castration.

Effect of Topically Applied Anaesthetic Formulation on the Sensitivity of Scoop Dehorning Wounds in Calves.

The post-operative effects of three formulations of topical anaesthetic and a cornual nerve block on the sensitivity of scoop dehorning wounds in calves were compared in two trials. In Trial 1, 21 female Holstein dairy calves aged 8 to 24 weeks were randomly allocated to two groups: (1) scoop dehorning with a post-operative application of a novel topical anaesthetic powder (DTAP, n = 10); and (2) scoop dehorning with a post-operative application of a novel topical anaesthetic ethanol liquid (DTAE, n = 11). In Trial 2, 18 castrated male and 18 female Hereford beef calves aged 16 to 20 weeks were randomly allocated to four groups: (1) scoop dehorning with a pre-operative cornual nerve block of lignocaine (DCB, n = 9); (2) scoop dehorning with a post-operative application of the novel topical anaesthetic ethanol liquid from Trial 1 (DTAE, n = 9); (3) scoop dehorning with a post-operative application of a topical anaesthetic gel (DTAG, n = 9); and (4) sham dehorning (CON, n = 9). Sensitivity was assessed by scoring the behavioural response of calves to stimulation of the wound or skin at time points before and after treatment. In Trial 1, DTAP calves had a greater probability of displaying more severe responses than DTAE calves at 90 and 180 min (P < 0.001). In Trial 2, at 1 h, DTAG calves had a greater probability of displaying more severe responses than CON calves. At 2 h onwards, all dehorned calves had a greater probability of displaying more severe responses than CON calves (P < 0.001). There were no differences between the responses of DCB, DTAG and DTAE calves at any time point. Topical anaesthetic formulations result in almost immediate but temporary anaesthesia of the wound following scoop dehorning in calves and may provide a practical option for pain relief on-farm.