Behavior of immunologically castrated barrows in comparison to gilts, physically castrated barrows, and intact male pigs

The behavior of immunologically castrated barrows (IC; with Improvest; Zoetis, Parsippany, NJ) was compared with that of intact males (IM), physically castrated barrows (PC), and gilts (G). The study used 160 commercial crossbred pigs in a randomized complete block design (blocking factor was start date of study) and was performed over an 8-wk period from 16 wk of age (67.2 ± 2.50 kg BW) to a final BW of 126.5 ± 6.05 kg. The first Improvest dose was given to IC at the start of the study (d 0), and the second dose was given 28 d later. Pigs were housed in single-gender groups of 4 and had ad libitum access to feed and water. General, aggressive, and sexual behaviors were observed over a 12-h period from 0600 to 1800 h by the same trained investigators on d −1 (d prior to first dose), 13, 27 (day prior to second dose), 34, 41, and 55 of study (end of test). General behaviors (number of pigs lying, sitting, standing, at feeder, and at drinker) were recorded every 10 min in all pens (10 pens/gender), and aggressive (bites, head butts, and fights) and sexual (mounts) behaviors were recorded continuously over the 12-h period on a sub-sample of 4 pens/gender. There was no difference (P > 0.05) between the genders for lying, sitting, or drinker-related behavior. For the 4-wk period prior to second dose, a greater percentage of PC and G were at the feeder (P < 0.05) than IC or IM (8.0%, 7.4%, 10.2%, and 9.3% for IC, IM, PC, and G, respectively; SEM = 0.44). However, after the second dose, the percentage of pigs at the feeder was similar (P > 0.05) for IC, PC, and G and was greater (P < 0.05) for those genders than IM (10.1%, 7.1%, 10.0%, and 8.8%, respectively; SEM = 0.50). Prior to the second dose, the incidence of aggressive behaviors was generally greater for IC and IM compared with PC and G; however, after the second dose, the incidence of aggressive behaviors was similar for IC and PC and lower (P < 0.05) for those genders than for IM. The frequency of mounts for IC was greater (P < 0.05) than for PC before (25.5, 27.3, 2.5, and 1.5 total mounts/pen, respectively; SEM = 4.37) but not after (P > 0.05; 3.3, 33.3, 0.25, and 0.25 total mounts/pen, respectively; SEM = 1.15) the second dose. These results suggest that prior to the second Improvest dose, the behavior of IC was similar to that of IM and transitioned to become more similar to the behavior of PC after the second dose.