† Shared piglet production rings typical of the Swiss pig production chain. AFP stands for the German “Arbeitsteilige Ferkelproduktion ”.
‡ Close production cycle farms are those performing all steps of pig production: gilt raising, breeding, weaning and fattening.

Live pig transport

The majority of farmers considered live pig trade as the most important mechanism of infectious disease introduction into, or spread from, their farm – except those owning closed production cycle farms, as they are rarely involved in pig trade. Recognizing the direct exposure to disease via introduction of new pigs, or indirect exposure via lorry contamination during transport tours performed by traders, they adopt different strategies to minimize this risk if possible. Mitigation strategies include trading as much as possible with the same farm or requesting to the trader that their farm should be the first one visited on a transport tour.
Awareness of the risks associated with pig transports via trading companies was not uniform among the interviewees. Four distinct clusters were identified with regards to farmers’ attitudes towards lorry drivers helping with the loading or unloading of pigs. Some farmers stated that drivers are aware of the most important biosecurity rules, and they never enter the stables. Other farmers expressed that lorry drivers do not access the stables, but that they need to be reminded (Table 2, quote from interview 4). The remaining interviewees revealed that drivers do enter their stables, either as an exception for difficult cases or as a regular and completely acceptable practice.
Not all farmers resorted to traders for pig transport. Self-performed transports are not as much exposed to contamination issues as trader transport tours, but they present alternative potential exposure mechanisms, due to the sometimes less professional practices compared to trader companies (Table 2, quote from interview 1). In our sample, three distinct situations were observed: farmers in the industrialized pig production areas of the country only do self-transports on rare occasions; farmers belonging to an AFP ring sometimes are not associated to a trader and perform transports personally; farmers with small holdings outside the main pig production areas perform all transports independently.
Although nowadays most Swiss breeding holdings practice artificial insemination, farms with traditional reproduction or farms outside the main production area still resort to natural insemination with a boar kept on the premises. Sharing boars with neighboring breeding farms as a courtesy between colleagues are susceptible to underreporting in the official national animal transport database, and they are always performed by farmers themselves with the aforementioned associated risks. During the interviews, three farmers confirmed that this practice still exists today (Table 2, quote from interview 5).

Farmer encounters

Many occasions for professional or social encounters between farmers were reported during the interviews, both on and out of the pig holdings. Farmers frequently mentioned that they are active in local, regional, or national farming associations and working groups. Regardless of the context, most interviewees strongly believed that meetings happening outside of their farming premises represent a very low risk for disease spread, as in those occasions they do not meet in work clothing (Table 2, quote from interview 1). Still, one interviewee revealed he would meet his colleagues in work clothing.
On-farm contacts with colleagues were also mentioned. For instance, a pig fattener said he occasionally goes to his neighbor’s pig stall to help him put down a sick pig (Table 2, quote from interview 12).
The sharing of pig and other farming equipment was also reported (Table 2, quotes from interviews 6 and 10). Most interviewees did not share pig farming equipment, either because they did not need to, or because they were afraid it would not be properly handled by other farmers. The most frequently shared pig farming items were narcosis tools for piglet castration and ultrasound machines for gestating sows. Other farming equipment, such as seeders, fertilizer spreaders and manure tanks, was shared more often.
Visitation to carcass collection points was reported by most farmers as a frequent task. Some of them said it is common to meet other farmers there, or even to help other farmers in the carcass disposal process (Table 2, quote from interview 17). During the interviews we identified three factors affecting the occurrence of this pathway: i) accessibility: limited opening hours may result in increased likelihood of farmer encounters while waiting for their turn to dispose of the carcass. Additional risky practices, such as asking other farmers to help in disposing carcasses, were encouraged by limited accessibility and farmers’ other engagements. ii) monitoring: according to the interviewees’ reports, some collection points are attended by personnel, some have a camera monitoring system, and some are not monitored at all. Some farmers expressed their concerns about the lack of monitoring as they believed it encouraged risky practices among their colleagues. iii) farmer’s risk perception: we encountered very different perceptions, ranging from feeling very relaxed during the disposal process, to considering visits to collection points as the most dangerous task for the health of their herd.

External collaborators

If the carcasses to be disposed of are heavier than a certain threshold weight (usually 200 kilograms), carcass disposal companies pick them up on the premises. To avoid incurring in the risk of contamination due to the collection trucks visiting several holdings on the same day, some farmers refrained from using this service and would rather manage the disposal on their own (Table 2, quote from interview 20).
According to the interviewees, pig feed advisors and veterinarians are external collaborators frequently visiting pig holdings. Both professionals are often granted access to the pig stables by farmers, and both may visit multiple stables within the same day. Depending on the level of observance of biosecurity protocols by themselves and the farmers, they may act as pathogen vectors. In our sample, not all farmers were visited by feed advisors. In the case in which they were, the stated frequency of visits varied from “once in a while” to “every one or two months”. As for veterinarian visits, most farmers received visits for official controls or from farm veterinarians. The frequencies of these visits ranged between “rarely” and “often”, the latter mostly due to piglet castration. While several farmers revealed their fear of disease introduction in the farm via veterinarians (Table 2, quote from interview 14), only one farmer shared his worries about his feed advisor possibly bringing pathogens into the stables.
The management of manure produced on the farm is also a task requiring the support of external collaborators. Liquid manure was reported to be transported by specialized companies (Table 2, quote from interview 21). The fact that these companies handle biological material from pigs and visit several farms on the same day, make them another possible carrier of pathogenic agents. Feed delivery trucks represent a similar risk due to multiple farm visits and the potential spread of pathogens by, for example, picking up dirt from a farm with truck wheels and subsequently depositing it in other locations. Some farmers recognized this risk and adopted preventive strategies such as ordering large amounts of feed to reduce the number of feed delivery trucks or placing feed silos far from the main premises in order to avoid truck contamination.

Environment and other contacts

Presence of wild boars in areas with high density of pig holdings may facilitate farm-to-farm spread of pathogens affecting domestic pigs. Most farmers reported that wild boars were spotted in the vicinity of their holding by themselves or their neighbors. The sightings occurred in all regions where the interviews took place. Farmers with pigs having outdoor access shared their concerns about not being prepared to prevent contact with wild boar because, for instance, of the lack of double fencing around their farm. Some of them justified their unpreparedness by the absence of wild boar in their region up to recent times (Table 2, quote from interview 16).
Other wild animals (e.g., rodents, birds) and pets (mainly cats) were frequently reported by farmers as being able to access the stables and potentially move from farm to farm in a short time frame. Only one farmer named such contacts in the context of potential infectious disease transmission. This interviewee believed his holding is well protected from infectious disease exposure but mentioned wild animal contact as the most probable mechanism of disease introduction.
Visits by non-professional external persons were often mentioned, for instance in the context of the direct sale of farm products on the premises, or because of the farmers’ will to show their farm to people expressing an interest in it (Table 2, quote from interview 5).
Table 2 Exemplary quotes from farmer interviews. A quote is given for each potential disease pathway that was identified or discussed with farmers during interviews. Sentences were translated to English from the original languages of the interviews.