Evaluation of pain and stress in three-week old piglets in relation to route of vaccine administration

Public opinion sees safeguarding the welfare of food-producing animals as a fundamental issue. Reducing pain during routine procedures has gained increasing attention accordingly. The aim of this study was to evaluate piglet behavioral and physiological response during vaccine administration, by comparing intramuscular injection with needle (IM) and intradermal injection without needle (ID). In this study, video and audio recordings were made at the time of vaccination on 53 piglets for IM and 53 piglets for ID in order to quantify their reactions (attempts at flight) and vocalizations (number and intensity), while cortisol analyses were performed on blood samples collected from a subsample of 18 piglets per treatment. Statistical analysis of the variables collected from video and audio files showed significant differences between the two treatments. At the time of vaccination, no flight reactions were shown by 90% of the ID piglets and 55% of the IM piglets (P<0.001). Eighteen percent of the IM pigs continued fidgeting after vaccination, while the ID pigs did not (P < 0.01). No vocalization was recorded in 55% of the ID piglets and in 25% of the IM group (P<0.008). Repeated screams were recorded for 13% of the piglets of the ID group and 50% of the IM group (P<0.001). Detailed analysis of the vocalizations also revealed longer length (IM = 588 ms vs. ID = 352 ms, P = 0.010) and higher maximum peak (IM = 99.8 dB vs. ID = 90.7 dB, P < 0.001) in the IM group compared to the ID. In conclusion, both during and immediately after vaccination, a lower frequency of behavioral aversive responses was observed in the ID route of vaccine administration group than in the IM group.