Surgical castration is a common management practice performed on male pigs to prevent the occurrence of boar taint and aggressive behaviors. Surgical castration is known to cause biological and behavioral changes in pigs indicative of pain, however, it is a procedure that is commonly performed without pain relief. Several methods of pain relief are known to reduce or eliminate the pain caused by castration, such as injecting a local anesthetic, but the disadvantages of this method is that animals need to be handled twice and the procedure has to be conducted by a veterinarian. The purpose of this study was to evaluate practical methods of pain relief that would benefit the welfare of the pig as well as be easy to perform by the handler. Therefore, in the present study we wanted to determine if general anesthesia induced by carbon dioxide gas (CO2) or analgesia elicited by giving a non-steroidal anti-inflammatory drug (NSAID) would reduce the pain caused by castration. The advantages of using carbon dioxide as a form of anesthesia include, the speed at which carbon dioxide can be administered, the speed at which animals return to consciousness and the fact that carbon dioxide is not a restricted drug that has to be administered by a veterinarian, and lastly there are no issues with drug residues. The advantages to using an NSAID is that they can be administered intramuscularly and there are NSAIDs (e.g. Banamine®) that are approved for use in swine in the US. Furthermore, both of these methods can be administered by trained staff and the animal only needs to be handled once. The objective of this study was to evaluate the effectiveness of carbon dioxide gas (CO2) anesthesia and/or a non-steroidal anti-inflammatory drug (NSAID) to alleviate the pain caused by castration.
At 3 d of age, male pigs were either control handled (CON), castrated without pain relief (CAS), castrated and then given an NSAID (CAS+NSAID), anesthetized with CO2 and then castrated (CAS+CO2) or anesthetized with CO2 and given an NSAID at the time of castration (CAS+BOTH). Blood samples were collected prior to, and 30, 60, 120, 180 min, 24 h and 3 d after castration or handling for analysis of cortisol (a measure of activation of the hypothalamic-pituitary-adrenal axis), C-Reactive protein (CRP, a measure of inflammation) and substance-P (SP, a measure of pain) concentrations. This study was then repeated using the same treatment groups and the behavioral response to castration and handling were measured using live observations. Body weight was measured before and 24 h after administration of treatments and wound healing scores were recorded for up to 14 d after castration. Anesthesia and/or analgesia did not effectively reduce the cortisol response to surgical castration. Overall, CRP concentrations were greater in CAS and CAS+CO2 pigs as compared to CON and CAS+BOTH pigs. Sixty min after castration or handling, SP concentrations were greater in pigs given CO2 anesthesia (CO2, CAS+CO2 and CAS+BOTH) than CON, CAS, CAS+NSAID pigs. Pigs castrated without pain relief spent more time lying-without contact than all other treatments during the first 30 min after castration, but thereafter CAS+CO2 pigs spent more time lying-without contact than other treatments. During the first 30 min after the treatments were applied, CAS+CO2 pigs spent more time displaying pain-like behaviors than CON, CAS, CAS+NSAID and CAS+BOTH pigs. Change in body weight and wound healing score did not differ among treatments. Neither CO2 anesthesia nor a NSAID, given separately or combined, markedly reduced the pain-induced distress caused by castration in pigs. More research is needed to evaluate practical methods of pain relief for pigs on farm.
