Pain alleviation during castration of piglets: A comparative study of different farm options

Pain alleviation associated with castration of piglets is an important welfare issue. The present study compares the effect of different approaches and products suitable for farmer use, with the aim to alleviate pain due to castration in piglets. A randomized within-litter design, with 28 replicate litters, compared 7 treatments: handling (H) restraint of the piglet and manipulation of the scrotum, castration without pain relief (C), 2 treatments (T2, T6) with different concentrations of tetracaine (2 and 6%) applied topically 10 min before and immediately post-surgery, and 3 treatments with i.m. injection of different nonsteroidal anti-inflammatory drugs (NSAID) 10 min prior to surgery (M-meloxicam, K-ketoprofen, TA-tolfenamic acid). Efficacy of pain relief was assessed during a 300 min period after castration by serum cortisol, behavior (walking, lying, suckling, in the nest, isolated and pain related: tremors, rubbing the rear, hunching, wagging of the tail), facial expression and scrotal skin pressure sensitivity. C pigs had greater serum cortisol concentration than all other groups at 60 min post-surgery (P < 0.001), while H pigs had lower concentrations than pigs given topical anesthesia (P < 0.001) though not injected analgesia. No treatment differences were significant at 180 min, but at 300 min cortisol concentration was greater in T2 and T6 piglets than those given NSAIDs (P = 0.03). These treatment differences were mirrored by the pressure sensitivity of the scrotum; in comparison with C piglets, those given NSAIDs showed a reduced sensitivity (P = 0.003) but those given local anesthesia did not (P = 0.15). C pigs showed increased frequency of painrelated behavior in the first 30 min in comparison with all other treatments, more time isolated than H or NSAID treatments, and more time standing inactive than H or K treatments. No behavioral differences were apparent after 60 min. No differences in facial expressions were observed among treatments. In conclusion, on-farm methods for pain relief can provide some, though not complete, pain alleviation in the hours after castration. The use of topical anesthesia gave only minor benefit in comparison to NSAID agents injected prior to castration. Since the main differences in indicators of pain between positive and negative controls were observed within the first h after castration, it is important to select drugs that act quickly after administration to facilitate practical processing schedules on farm.