The development of pain in young pigs associated with castration and attempts to prevent castration-induced behavioral changes

Four experiments were conducted to examine the development of castration-induced behavioral changes, the effects of castration age on pig weight gain, and the efficacy of common analgesics for use in castrated pigs. In Exp. 1, behavioral changes associated with castration of pigs at 1, 5, 10, 15, or 20 d of age were evaluated. Castration caused measurable changes (reduced suckling, reduced standing, and increased lying times, P < .05) in the behavior of young pigs compared with that of intact pigs at all ages tested. Effects of age and interactions between age and castration treatment were not significant (P > .10) for any behaviors evaluated. In Exp. 2, the performance of pigs castrated at 1 d of age was compared with the performance of those castrated on d 14 and female littermates. Birth weights, weaning weights, and mortality were recorded. Pigs that were castrated on d 14 were heavier (P = .05) at weaning and had a higher (P < .05) weight gain during lactation compared to pigs castrated on d 1 of age. Pig mortality was similar among the treatments. In Exp. 3 and 4, the efficacies of pain-reducing drugs (non-narcotic analgesics) were evaluated for effectiveness in reducing castration-induced behavioral changes in 8-wk-old pigs. Although castration reduced (P < .05) feeding time and weight gain, neither aspirin nor butorphanol influenced behavioral changes associated with castration. We conclude that pigs show similar behavioral changes (and probably pain perception) when castrated from 1 to 20 d of age. However, pig performance data favored castration at 14 d rather than at 1 d of age. Among older pigs, which show much greater behavioral effects of castration, analgesics (aspirin and butorphanol), used at recommended doses, provided no measurable effect on castration-induced behavioral changes.