Abstract Male piglets raised in the United States commonly undergo surgical castration to improve future meat quality. The procedure is painful and there is a need for easy-to-use, effective, and affordable castration pain-mitigating products. This preliminary study’s objective was to evaluate the use of a topical gel containing 33% oleic acid for reducing castration pain. We hypothesized that the oleic acid gel would reduce pain behavior and physiological stress in piglets following surgical castration. At 2 days of age, 12 piglets were enrolled and allocated to 1 of 3 experimental treatments: 1) non-treated castration (CONTROL; n = 4), 2) scrotal lidocaine injection prior to castration for short-term pain relief (LIDO; n = 4), or 3) scrotal topical oleic acid gel application immediately after castration (GEL; n = 4). All castration treatment procedures occurred on experimental day 0 (5-7 days of age). Pain-related behavioral data were collected on days -1, 0, +1, and +2 relative to the castration procedure. Specifically, each piglet was observed for 60 minutes each day from 1400-1500 h. Postural behaviors (standing, lying, sitting) were collected using a 2-minute instantaneous sampling method. Pain-related behaviors (hind-leg lifting, tail wagging) and nursing were observed continuously. Nine experimental piglets (n = 3 from each treatment) underwent heart rate variability (HRV) collection for a period of 60 minutes between 0900-1330 h on each of the behavioral data collection days. Average inter-beat interval length (RR), standard deviation of inter-beat interval length (SDNN), and root mean square of successive differences (RMSSD) were measured. Data were analyzed using PROC GLIMMIX in SAS 9.4. Treatment did not affect time spent lying (P = 0.73), sitting (P = 0.23) or standing (P = 0.62). There was an effect of experimental day on standing behavior, where time spent standing was greater on d + 1 compared to d -1 (P = 0.0002), d 0 (P 0.0001), and d + 2 (P = 0.02). Standing behavior was also greater on d + 2 compared to d 0 (P = 0.02). Treatment did not affect tail wagging (P = 0.18) but tended to differ for hind-leg lifting, where GEL piglets exhibited a greater hind-leg lifting count compared to LIDO piglets (1.68 ± 0.43 vs. 0.19 ± 0.43; P = 0.08). Time spent nursing and nursing bouts were not affected by treatment (P 0.6). No treatment effects were observed for RR (P = 0.46), SDNN (P = 0.50), or RMSSD (P = 0.81). However, RMSSD tended to be higher on experimental d 0 compared to d -1 (P = 0.06) and d + 2 (P = 0.10), regardless of experimental treatment. In conclusion, topical application of an oleic acid gel following surgical castration had no clear effect on piglet behavior or HRV.
Seevers et al. (Wed,) studied this question.