Assessment of ractopamine supplementation and immunization against GnRH effects on behavioral traits and human-pig interaction in heavy weight market gilts

•Ractopamine supplementation did not entail aggressive behavior towards a pen mate.•Immunized gilts showed behaviors indicative of investigation.•Immunization against GnRH does not seem to be negative for the welfare of gilts. Immunocastration (IM) has recently emerged as an alternative for rearing gilts up to heavier slaughter weights, considering its effects on performance improvement and sexual behavior suppression. The interaction between IM and ractopamine (RAC) supplementation is reported to be beneficial for growth and carcass characteristics. However, some studies reported RAC’s adverse effects on swine behavior, mainly by increased aggressiveness. The aim of the present study was to evaluate interactive effects of IM and RAC on behavioral responses in heavy weight market gilts. Seventy-two gilts (2 gilts/pen) were used to measure the behavioral characteristics and human-pig interaction parameters during the finishing phase. The factorial arrangement was defined as two RAC levels (0 and 10 mg/ kg of diet) by two immunization categories (non-immunized and immunized gilts). The first and second immunizations were performed at 15 and 19 weeks (wk) of age, respectively. RAC supplementation occurred from 21 to 25 wk of age, when all gilts were daily exposed to sexually mature boars. Animal behavior, observed for 24 h, and the interaction between gilts and an observer positioned inside a test pen were evaluated at a single time point (23 wk of age). There were no treatment effects on time spent eating, drinking, lying, fighting, sitting or mounting (P > 0.05) during the 24-hour period. IM (−32.4%, P