Consequences of Immunization Against Gnrf and Ractopamine Supplementation on Behavioral Traits of 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 increased aggressiveness. Seventy-two gilts (2 gilts/pen) were used in order to measure the interactive effects between IM and RAC on behavioral characteristics and on human-pig interaction 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 immunization were performed at 15 and 19 weeks of age, respectively. RAC supplementation occurred from 21 to 25 weeks of age, when all the gilts were exposed to mature boars daily. Animal behavior (on a 24-hour basis) and the interaction between gilts and an observer positioned inside a test pen were both evaluated at a single time point (at 23 weeks of age). There were no treatment effects on time spent eating, drinking, lying, fighting, or mounting (P > 0.05) during the 24-hours period. Both RAC (-21.6%, P < 0.05) and IM (-32.3%, P < 0.01) caused a reduction in standing behavior and there was an interaction between IM and time for sitting behavior (P < 0.01), where immunized gilts concentrated this behavior from 4:00 PM to 8:00 PM (2.11%), with a peak at 6:00 PM (3.89%). 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 (-67.38 sec, P < 0.001) and approached the observer (-125.47 sec, P < 0.001) in a reduced time compared to non-immunized gilts, regardless of RAC. The type of interaction between animals and the observer was graded from 1 to 5 (1 = soft contact with the observer and 5 = pigs aggressively tweaking on the observer’s clothes) and 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. Assessment of comportment traits in a larger number of animals, under commercial conditions, merits further investigation.