Support for stalls varied across the demographic categories. Before the provision of additional information, univariable analysis showed that U.S. residents were more supportive of stalls than were Canadians (P<0.03) and participants with less education were more supportive of stalls (P<0.02). In the multivariable analysis only education was significant (P<0.04). After the provision of information, univariable analysis showed similar effects of participant residency (P<0.03) and education (P<0.03), and also showed that males were more supportive of stalls than were females (P<0.01); the multivariable analysis also showed effects of gender (P<0.04) and education (P<0.05).

The decline in support after additional information was also consistent across most demographic categories, specifically across both males and females, both U.S. and Canadian residents, and for all three levels of education ( Table 2 ). Support also declined after the provision of information for the younger participants (19 to 29 and 30 to 39); there was no decline for the older participants, but support for stalls was already low for these individuals.

Results are shown in relation to participant demographics. The participants shown here were recruited via Mechanical-Turk and provided demographic information (n = 133). Participants responded to the question “Do you believe that pregnant sows should be housed in gestation stalls or in groups?”.

One strength of our methodology was the use of independent groups. Each of the groups was exposed to a different set of participant comments, allowing us to assess the generality of our results. In each of 8 replicate groups recruited using Mechanical Turk, most participants did not support gestation stalls before the provision of the additional information (support ranged from 0.0 to 44.5% support for stalls; moderate and strong support combined, see Table 2 ). After the provision of information, support declined in five of the groups, stayed the same in two groups and increased (by one participant) in one group.

Respondents were able to consider as many different sources of additional information as they desired. The majority of respondents reported having looked at images or videos of either gestation stalls or group housing for pregnant sows (121/135). Thirty-two percent said they looked at one or both scientific papers; the same number also reported reading the frequently-asked-questions page.

Responses were provided before the provision of additional information and after participants had the opportunity to view images, videos, scientific review papers, and a frequently-asked-questions page. Each cell shows the number of participants (out of a total of 135 respondents recruited via Mechanical Turk) adopting each pair of responses. The number in parentheses in the left-hand column shows the before totals and the number in parentheses in the column headings shows the totals after respondents had viewed the additional information.

Fig 1. Responses to the question “Do you believe that pregnant sows should be housed in gestation stalls or in groups?”

Considering only the Mechanical-Turk participants ( Fig 1 ), prior to the provision of additional information, 55.6% supported group housing (moderate and strong support), 30.4% supported gestation stalls (moderate and strong support), 3.7% of respondents were neutral, and 10.4% did not support either system. Contrary to our prediction, the provision of additional information generally reduced support for the use of gestation stalls ( Fig 1 ; P<0.001). In particular, more people strongly supported group housing after accessing information (84/135) than before (55/135). Of the 88 participants who maintained their position after the provision of additional information, most (53) were the strong supporters of group housing.

Qualitative analysis

The comments provided by participants provided insights into why they changed their response after viewing the information. Below we describe these comments in relation to the participant’s original response.

The majority of participants who were moderate in their support of either system, or who were neutral on the issue, changed after accessing sources. The following comment is from one participant who was initially a moderate supporter of group housing and who became a strong supporter of groups: “…after seeing photos of the stalls…I believe they should be housed in groups because it’s the best of two bad choices.” (8; [0.7])

A moderate supporter of gestation stalls initially justified stall housing with this comment:“It seems that this method has been working since the 1950s, and I believe it is important to avoid the spread of diseases above all, especially if the pigs are used for meat.” (4; [3.25]) After accessing addition information the same respondent wrote: “I did not realize that the stalls were so small. Knowing the size of the stalls, I think it is completely unfair and unreasonable to leave a pregnant pig unable to move for part or all of the pregnancy.” [10.5]

Two participants who strongly supported groups before accessing additional information became moderate supporters of gestation stalls. One of these participants remarked that, “The sight of the wounds caused due to grouping makes me change my reason.” (6; [1]) One participant who strongly supported gestation stalls before the provision of information became more moderate in their support of gestation stalls, and another switched to moderate support for group housing. The latter of these two participants described their reason for switching: “I thought that the gestation stalls would be cleaner and have more room but they were tiny and they said the sows stayed in there for the duration of their lives, so it's probably better for them to be housed in groups.” (8; [1.2])

Nine of the comments relating to change were made by respondents who did not actually change their decision. Of these, 7 were from strong supporters of group housing, 1 from an individual who did not support either system, and 1 from a moderate supporter of stalls. These participants claimed that the information either had no effect or that it intensified their position. For example, one strong supporter of group housing commented: “Viewing the images of sows in gestation stalls renewed and strengthened my opposition to them.” (2; [1])

The comments provided by participants also provided insights into their reasons for supporting different methods of sow housing. Many of the comments focused on one or more of three types of concerns: physical health (e.g., disease and injury), the ability to live in a “natural” manner (e.g., ability to perform natural behaviors and live in environments with natural elements), and affective states (e.g., pleasure and pain) (Table 3). We describe the themes raised by participants that supported gestation stalls, and then describe themes raised by supporters of group housing.

Below we describe each theme and the number of comments within decision category (e.g., strong or moderate support of either system) that referenced these. Moderate and strong supporters of stalls tended to highlight concern for physical health, including spread of disease (7/19 comments), the importance of individual monitoring of sows (5 comments), and issues associated with injuries and aggression (11 comments). For example, one strong supporter of gestation stalls said:

“I grew up on a farm where we originally had sows housed in groups and they were very aggressive toward each other. We later changed to gestation stalls and both the sows and their offspring were in better health and were less stressed than they had been in groups.” (8; [1.5])

Concern for the animals’ safety and ease of labor were voiced by a moderate supporter of gestation stalls: “I think the lowering of aggression, and the fact that the workers can individually monitor [the sows] sounds nice.” (7; [9])

Moderate supporters of stalls tended to prioritize protection from injury or disease, although one moderate stall supporter acknowledged that there may be a need to provide for social interaction:

“They are being raised for food, which means that curbing disease and injury is in the best interest of those involved; however, if they are to be bred repeatedly, it raises the question of what manner of social structure pigs form naturally. If it would be beneficial for them to be kept in a group of other animals…it should be considered.” (3; [4])

Some gestation stall supporters described the need for the management of animals and their environments. A moderate supporter of stalls suggested that domestication may have reduced how much sows benefit from social interactions:

“They [sows] evolved to live in social packs out in the wild [but] have been bred …away from that, and their lives are nowhere close to what they are in the wild. Having them congregate while pregnant at the cost of injuries and disease is a token gesture that does nothing to actually help the pig and does much to hurt the farmers.” (6; [1])

Concern for the affective states of sows was mentioned in just two comments from stall supporters. For example, one moderate supporter of gestation stalls said that stalls were, “ok only if…the sow does not show any signs of pain.” (9; [3])

Supporters of group housing (moderate and strong support) favored the ability of pigs to interact socially, even if this occasionally resulted in some competitive or aggressive behavior. Thus when these participants mentioned aggression (14/58 comments) they mainly focused on how management of groups could prevent the problem. These comments focused on stocking density, group composition, and approaches to feeding that reduce aggression. For example, one respondent who strongly supported groups suggested:

“The only reason sows are aggressive in group housing is because the [sows] …are crowded in small enclosures where they feel the need to be territorial. I’ve raised pigs and as long as they have adequate space and things to do (root, nest, etc.) they are very rarely aggressive enough to cause injury.” (5; [5])

Another questioned the assertion by some supporters of gestation stalls that group housing puts animals at risk for aggressive interactions:

“…Why does group housing risk aggressive behavior? Perhaps the group housing situations are too constrictive? Or could it be that pregnant sows need ‘areas of refuge’? Maybe we should look at what group housing looks [like] instead of assuming that gestation [stalls] are the only alternative.” (2; [1])

Moderate and strong supporters of groups often commented on the benefits of social interaction (28/58 comments), space for greater movement (13 comments), expression of natural behavior (14 comments—including 5 comments on rooting and nesting behaviors). For example, one respondent commented:

“Pigs are social animals and I think they should have the opportunity to engage in social interactions with other pigs or decide [when] they want to be alone. As well, pigs need an area to walk about and have the opportunity to perform behaviors they are motivated to do.” (1; [6.6])

Five comments focused on the idea of natural environments and the pigs’ ‘nature’, with the majority of comments reflecting the belief that a good life for animals could be achieved by minimizing human interference or emulating nature. Moderate and strong supporters of groups used language that expressed a desire to see sows “live naturally” and referred to living conditions of wild pigs to support their assertion that sows’ adaptive behaviors are thwarted in certain captive settings. One strong supporter of group housing situated the issue of behavioral deprivation in the context of evolution:

“Ethological studies have proven again and again that removing animals from their natural conditions causes stress. Pigs have evolved for thousands of years to be herd animals…To confine a sow, apart from the direct, physiological cruelty inherent in such a situation is [to force] her into a situation which goes against all of her natural instincts (namely to root and forage with a herd).” (2; [7])

The comment above, while focused on living naturally, also references concern for sows’ mental and emotional states. Nine other comments referred to the sows’ capacity to feel stress, pain, and happiness.