In Europe, a culling rate of around half of the sows per herd per year is not unusual, which means that millions of sows are transported to slaughter each year. They are all transported by road. The specific welfare risks of transporting cull sows to the abattoir are addressed in a European Union Reference Centre for Animal Welfare Pigs (EURCAW-Pigs) review.

Across the different pig categories, transport is a multifactorial stressor, with effects on all pig types. Some scientific attention has been directed towards the cull sow category, forming the basis of the EURCAW-review. Among the primary concerns for the welfare of cull sows during transport are (a) the sensitivity of these animals towards heat stress; (b) fitness for transport; and (c) the tendency of sows to fight when mixed with unfamiliar conspecifics. Based on findings such as increased mortality upon arrival at the abattoir compared with finishers, sows are considered more vulnerable towards transport than most other pig categories.

Heat stress

The reproductive status of sows affects their susceptibility to heat stress, and ongoing milk production probably is a risk factor compared to dry animals. Sows can be sent to slaughter at all stages of the reproductive cycle (except for the last 10% of pregnancy (according to Council Regulation 1/2005), and in some MSs, sending sows to slaughter in the last 30% of pregnancy is prohibited by national legislation. In the days just before and after weaning of the piglets, lactating sows are especially sensitive to heat stress, as their milk production is very high at this stage.

Fitness for transport

In 2022, EFSA concluded that questions about fitness for transport are among the major concerns for sow welfare during transport. Due to the general health impairment of a large proportion of cull sows, compared to average finishers, sows may experience a higher risk of worsening of pre-existing health conditions, as well as a higher risk of new health conditions occurring during transport.

Fighting between sows induced by the mixing of unfamiliar individuals

Under natural conditions, sows live in groups of related individuals. Within a group, a hierarchy preventing overt fighting between group members exist. Under production conditions, sows are frequently mixed with non-penmates, a management practice that has received considerable scientific attention. It is well-documented that sows – when mixed with unfamiliar individuals – will fight to re-establish a hierarchy, and that the fighting can be severe and of considerable duration. Consequently, the mixing of unfamiliar sows has long been recognised as a welfare problem, mainly due to inter-sow aggression. Therefore, fighting among sows is considered a “focus area” for inspection. 

During transport of sows, mixing of unfamiliar animals is almost unavoidable and can have consequences for the animal welfare. Even though documentation as such is currently missing, it is highly likely that sows will fight during transport, when mixed with unfamiliar individuals. This behaviour can challenge the continuous fitness for transport, increase the risk of heat stress, and thus challenge the overall welfare of the sows. In an unpublished study in Denmark, Kobek-Kjeldager et al. (in prep.) found that almost 80% of the sows initiated aggressive interactions during the journey and only a few never received aggression when they were transported to slaughter, under commercial conditions with 12 sows per truck compartment.

Scientific evidence on reducing the level of aggression in pick-up facilities or pick-up vehicles is not available. However, it has been suggested that the consequences of mixing in terms of aggression and injury can be mitigated to some extent by reducing group size and by ensuring enough space for subordinate individuals to move away from aggressive ones. Further studies involving cull sows are needed to verify whether initiatives like that can limit the occurrence of fighting – during the preparation phase and later in the journey when sows are transported to slaughter.

In the review on transport of sows, the scientific knowledge about sow transport is reviewed against the background of the relevant European legislation, including a discussion of preparation for transport, how sows are picked-up by vehicles and the journey to an abattoir. The final part of the review covers relevant legislation as well as the proposal of potential indicators of sow welfare during transport.