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The aim of this study was to investigate the effect of sow confinement and nonconfinement during parturition and early lactation on the performance of sows and piglets prior to weaning. Sows and their litters were housed in either a conventional farrowing crate (control; 1.7 × 2.4 m) or a swing-sided pen (2.8 × 2.15 m). Sows housed in the swing-sided pen had the crate open (open) or closed (closed) during farrowing and opened on d 3 (LAC3) or 7 (LAC7) of lactation. Data are means ± SEM. The numbers of total and live-born piglets were not different between treatments and averaged 13.1 ± 0.4 and 12.3 ± 0.2 piglets/litter, respectively. Sows housed in a farrowing crate had a greater (P= 0.03) number of stillborn piglets compared with open sows from pens (1.1 ± 0.2 vs. 0.6 ± 0.1 piglets/litter, respectively). Live-born piglet mortality before litter equalization on d 1 was greater (P< 0.01) for open sows compared with closed and control sows (1.6 ± 0.2 vs. 0.9 ± 0.2 vs. 1.1 ± 0.1 piglets/litter, respectively) and was largely explained by an increase in the incidence of piglets overlain (P< 0.01) in the open compared to closed and control sows (1.3 ± 0.1 vs. 0.5 ± 0.1 vs. 0.8 ± 0.1 piglets/litter, respectively). Overlay mortality between d 3 and 7 of lactation was greater (P= 0.03) in LAC3 sows compared to LAC7 and control sows (0.4 ± 0.1 vs. 0.2 ± 0.1 vs. 0.2 ± 0.1 piglets/litter, respectively). Treatment did not affect either the incidence or cause of piglet mortality after d 7 of lactation (P> 0.05). Total live-born piglet mortality from birth until weaning for the control, closedLAC7, closedLAC3, openLAC7, and openLAC3 was 1.86 ± 0.19, 1.95 ± 0.23, 2.10 ± 0.39, 2.45 ± 0.27, and 3.74 ± 0.48, piglets/litter, respectively. Total live-born piglet mortality from birth until weaning was greater in the openLAC3 and openLAC7 treatments compared to control (P< 0.01), and openLAC3 was also greater than openLAC7, closedLAC3, and closedLAC7 (P< 0.01). The current data indicated that reducing sow confinement during parturition decreased stillborn number but increased live-born piglet mortality compared to a farrowing crate, and removing confinement on d 3 of lactation further increased total piglet mortality compared to removing sow confinement on d 7 of lactation in sows that farrowed open. Sows that were confined during farrowing and until d 3 or 7 of lactation in a swing-sided pen had a similar piglet mortality compared to those in a farrowing crate.

Aggression between domestic sows is greatest when sows are first introduced to each other and hierarchies form. The aim of this study was to determine the effect of a spacious “mixing pen” on sow aggression and stress. Sows were mixed into groups of 6 and allowed 2 (LOW; 8 groups and 48 sows), 4 (MED; 7 groups and 42 sows), or 6 m2/sow (HIGH; 7 groups and 42 sows) for 4 d after mixing, at which point all pens were equalized to 2 m2/sow. Salivary cortisol concentration and injury counts were measured on d –1, 0, 1, 3, and 4 relative to mixing, and behavior was also recorded on each of these days following mixing. Reproductive performance was assessed at farrowing. A linear mixed model was applied to the data. Data are presented as least squares means and standard error of the mean. Where transformations occurred, nontransformed adjusted means are presented in parentheses following the presentation of transformed data. In the primary analyses where measures were considered at the pen level, there were no effect of space allowance on fight number per sow, duration of fights, percentage of total time spent fighting, displacements, bites, knocks, and lunges (P> 0.05). These measures were higher on d 0 (i.e., fight number 1.0 ± 0.1 [13.8]) compared with d 1 (0.4 ± 0.1 [4.2]), 3 (0.7 ± 0.1 [5.3]), and 4 (0.7 ± 0.1 [5.5]; P< 0.05), with no increase in aggression on d 4 when pen sizes were standardized (P> 0.05). There was increased percentage of time spent active (1.5 ± 0.02 [33.7] for LOW, 1.5 ± 0.02 [36.5] for MED, and 1.6 ± 0.02 [43.4] for HIGH) and time spent exploring (1.8 ± 0.1 [3.5] for LOW, 2.0 ± 0.1 [4.0] for MED, and 2.3 ± 0.1 [5.7] for HIGH) and number of nonaggressive sow–sow contacts (0.3 ± 0.09 [2.2] for LOW, 0.4 ± 0.07 [3.2] for MED, and 0.5 ± 0.07 [4.5] for HIGH) in HIGH compared with LOW (P< 0.05). Farrowing rate and total piglets born were not affected by treatment (P> 0.05). A secondary analysis was conducted that examined individual sow behavior within each pen, and this identified increased injury number in the lowest ranked sows (involved in no fights on d 0 and no displacements on d0 to d4) in LOW (9.3 ± 1.2 [107.9] for LOW, 6.2 ± 0.8 [53.0] for MED, and 5.1 ± 0.8 [28.1] for HIGH) and also decreased fight number and duration in HIGH compared with LOW on d 0 and 1 (P< 0.05). Our primary data analysis demonstrates positive exploratory and social behaviors with increased space and suggests that a reduction in space following hierarchy formation is not a significant stressor. Additionally, there is some evidence at an individual sow level that increased space at mixing benefits sow welfare parameters, especially for low-ranked sows.

Factors that have been shown to impact the welfare of group-housed sows are discussed in this review. Floor space allowance markedly affects sow welfare. In addition to quantity of floor space, the quality of space is important: spatial separation between sows can be provided with visual or physical barriers and stalls. Whereas 1.4 m2/sow is insufficient, further research is required to examine space effects in the range of 1.8 to 2.4 m2/sow in more detail. The period immediately after mixing has the most pronounced effects on aggression and stress, and therefore, well-designed mixing pens offer the opportunity to reduce aggression, injury, and stress while allowing the social hierarchy to quickly form. Because hunger is likely to lead to competition for feed or access to feeding areas, strategies to reduce hunger between meals through higher feeding levels, dietary fiber, or foraging substrate should be examined. However, feeding systems, such as full-body feeding stalls, can also affect aggression and stress by providing protection at feeding, but deriving conclusions on this topic is difficult because research directly comparing floor feeding, feeding stalls, and electronic sow feeder systems has not been conducted. Familiar sows engage in less aggression, so mixing sows that have been housed together in the previous gestation may reduce aggression. Although there is evidence in other species that early experience may affect social skills later in life, there are few studies on the effects of early “socialization” on aggressive behavior of adult sows. Genetic selection has the potential to reduce aggression, and therefore, continued research on the opportunity to genetically select against aggressiveness and its broader implications is required. Most research to date has examined mixing sows after insemination and knowledge on grouping after weaning is limited.