Effects of previous housing system on agonistic behaviors of growing pigs at mixing

Abstract

Previous studies indicated that rearing environment in early life affects behavioral development, which consequently modifies behavioral response of pigs to stressful environments in later stages of the production. A study was conducted to investigate effects of group-farrowing system on behavior of growing pigs at mixing. A total of 216 pigs at 8 weeks of age from one farrowing batch were used, with equal number of pigs that were born and reared in a group-farrowing system and in a confinement system. In the group-farrowing system, pigs were farrowed in bedded individual pens, and mingled into a group of eight litters at about 10 days of age. Pigs were weaned at 5 weeks, and remained in groups of 81 (±2.6) in the group-farrowing barn until 8 weeks of age. In the confinement system, pigs were born in farrowing crates, mixed and moved to pens of nine pigs in a confinement nursery at weaning (5 weeks of age). At 8 weeks of age, all pigs were allocated into 24 pens of nine pigs in a confinement grow-finish barn, with 12 pens from each previous housing system. The familiarity among pigs within a pen was maintained the same between the two housing systems. Aggressive interactions among pigs in six pens of each housing system were video-recorded for 24 h immediately after mixing. The videos were viewed continuously to register all fighting events. The total duration and the frequency of fighting, fighting among familiar and unfamiliar pigs, and fighting occurring at feeders, the drinker, and in the open area of the pen were registered. Data were analyzed by using the Glimmix procedure of the SAS with pen as the experimental unit. The total duration (19 versus 120 s/h, P = 0.001) and the frequency (1.5 versus 3.8 fights/h, P = 0.002) of fighting was less among pigs originated from the group-farrowing system, compared with pigs from the confinement system during the 24 h period after mixing. The majority of fighting was observed in the open area and at feeders, with pigs reared in the group-farrowing system fighting less than pigs reared in the confinement systems in these locations. Only 5% of total fighting time occurred among familiar pigs, regardless of previous housing system. These results suggest that pigs reared in the group-farrowing system maintained the ability to discriminate between pen mates and non-pen mates, and were more tolerant of unfamiliar pigs when mixed in small groups compared to pigs reared in the confinement system.