Behavior of Piglets in an Observation Arena before and after Surgical Castration with Local Anesthesia

SIMPLE SUMMARY: Surgical castration of piglets is generally recognized as a painful procedure. Thus, for animal welfare reasons, the German Animal Welfare Act stipulates the use of effective anesthesia during castration. However, whether local anesthesia provides adequate analgesia has been an ongoing debate in Germany. In the present study, we compared the behavior of 178 piglets allocated to various test groups in an observation arena before any of the applied procedures, after administration of the local anesthetic, and 0, 2 and 24 h after surgical castration. The local anesthetic and the injection techniques were evaluated and optimized in three sequential study parts. Overall, the results revealed that when local anesthesia was used, piglets less frequently showed pain-associated behaviors—such as changes in tail position—than piglets of the control group that had been castrated without local anesthesia. Non-castrated piglets showed the fewest pain-associated behaviors in the observation arena. In several test groups, the piglets showed changes in tail position, tail wagging, or hunched-back posture on the day following the procedure. These behaviors differed significantly from those shown before the procedure. The administration of local anesthetics in the present study considerably reduced castration-related pain. However, because local anesthesia has a limited duration of effect, adverse effects due to castration-related pain were still observable one day after castration. ABSTRACT: Surgical castration of piglets is generally recognized as a painful procedure, but there is currently no gold standard for the assessment of pain behavior in piglets. However, pain assessment is essential for evaluating the effectiveness of local anesthetics. In this study, we investigated the efficacy of four local anesthetics in terms of pain relief during and after surgical castration in three sequential study parts. To do so, we filmed 178 piglets before the applied procedures, after injection of the local anesthetic, and up to 24 h after castration (five observation times in total) in an observation arena and compared their behavior before and after castration and between treatments and control groups. The results showed significant differences in the behavior of the piglets before and after castration and between the sham-castrated control group and the control group castrated without anesthesia. The different local anesthesia treatment groups showed diverging differences to the control groups. The most frequently shown pain-associated behaviors of the piglets were changes in tail position and hunched back posture. We observed a reduction but no complete elimination of the expressed pain-associated behaviors after local anesthesia. Several behavioral changes—such as changes in tail position, hunched back posture or tail wagging—persisted until the day after castration. Owing to the limited duration of the effects of the local anesthetics, local anesthesia did not influence long-term pain.