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Nitrous oxide by itself is insufficient to relieve pain due to castration in piglets

Rault, J.-L., Lay, D. C.
Journal of animal science 2011 v.89 no.10 pp. 3318
agitation, United States, weight gain, weaning, vocalization, tranquilizers, tail, sleep, skin tests, sedatives, reflexes, piglets, pain, nitrous oxide, models, humans, castration, anesthesia, analgesics, analgesic effect, air
Surgical castration is performed on most male piglets in the United States. However, castration is painful and analgesics have been considered to relieve pain. Inhalant gases with analgesic properties allow for a fast induction, have short-term and reversible effects, and are a needle-free option. Nitrous oxide (N2O; “laughing gas”) has been widely used in human surgery and dental offices as an analgesic, sedative, and anxiolytic drug, yet N2O has not been thoroughly investigated for use in farm animals. We hypothesized that the analgesic effect of N2O could reduce the pain experienced by piglets during or immediately after castration. Twenty-four male piglets, from 12 litters, were castrated at 3 d of age. One piglet received N2O and a littermate received air as a control. After 150 s of exposure to the gas, castration was performed while the piglet remained exposed to the gas. Agitation scores and total vocalization length were recorded during castration. Behavioral observations were continued for 3 d postcastration by using a 5-min scan-sampling method for 4 h the first morning and for 2-h periods in the morning and afternoon of each day thereafter. Body weight gain was measured on the day before castration, at 3 d postcastration, and at weaning. Data were analyzed using a mixed model in SAS (Cary, NC). Nitrous oxide successfully induced anesthesia in all N2O piglets, as validated by a skin pinch test and the loss of the palpebral reflex. Total vocalization length was shorter in piglets receiving N2O during the induction phase (P = 0.003) but was not different during castration itself because piglets receiving N2O awoke and vocalized as much as control piglets (P = 0.87). Agitation scores during the whole procedure were reduced in piglets receiving N2O in both frequency (P = 0.005) and intensity (P = 0.026). For 2 h after castration, piglets receiving N2O displayed less huddling behavior than did control piglets (P = 0.01). Over the 3 d, piglets receiving N2O performed more tail wagging (P = 0.02) and tended to show fewer sleep spasms (P = 0.06) than did control piglets. Piglets given N2O tended to have a reduced growth rate compared with control piglets at 3 d postcastration and at weaning (P = 0.05 and P = 0.06, respectively). Nitrous oxide was effective in inducing anesthesia in neonatal piglets during handling. Nonetheless, its analgesic effects appeared insufficient in preventing castration-induced pain.