Assessment of ractopamine supplementation and immunization against GnRH effects on behavioral traits and human-pig interaction in heavy weight market 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 < 0.01) caused a decreased frequency in standing behavior. Aiming to assess effects of IM and RAC on human-pig interaction, groups of four gilts within each treatment were exposed to an observer standing in the corner of a test pen. Immunized gilts both crossed a line distant one meter from the observer (−33.70 s, P < 0.001) and approached the observer (−62.70 s, P < 0.001) in a shorter time compared to non-immunized gilts, regardless of RAC. The type of interaction between animals and observer was not affected by treatments (P > 0.05). IM and RAC did not entailed any aggressive behavior on late finishing gilts and IM improved their willingness to approach and investigate. Therefore, the immunization of heavy market gilts against GnRH provides behavioral benefits regardless of RAC supplementation.