Confinement of sows at parturition increases the incidence of behaviours thought to indicate pain

As gestation progresses, a sow’s tolerance to pain is increased to the point that, immediately before and during farrowing, they are almost non-responsive to adverse stimuli (Jarvis et al. 1997). What is less clear, is the impact of the farrowing environment on this parturition-induced hypoalgesia. The aim of this study was to determine the impact of confinement during parturition on behavioural and physiological indicators of pain. We hypothesised that reduced confinement of the sow leading up to and during parturition would result in reduced pain-related behaviour.

Sows (Parities 1 to 3) were housed in ‘360 farrower’ pens (Midlands Pig Producers Ltd, UK), a design that fits the standard footprint of a traditional crate but has adjustable bars, which gives the animal space to move around but also enables containment. Two treatments were applied; OPEN: pen was open from sow entry (5 days before farrowing) until the sow stood for the first time following parturition, at which point they were closed, and CLOSED: pen was closed from sow entry. Blood was collected hourly via an ear vein catheter 24 h before the birth of the first piglet through until the birth of the last piglet and analysed for plasma cortisol concentration using radioimmunoassay (n = 18 CLOSED, n = 15 OPEN). Video cameras remotely collected footage during parturition (from the birth of the first until last piglet) for a subset of sows (n = 12 CLOSED, n = 14 OPEN). Behaviours indicative of pain (Ison et al. 2016) and stereotypies were analyszd using continuous sampling (Observer XT, Noldus, The Netherlands). A generalised linear model with poisson distribution was used for behavioural count data in SPSS v24.0 (IBM, Armonk, NY, USA). Cortisol data were analysed using a linear mixed model with sow id as the unit and time as the repeated-measure.

Animals that farrowed in the OPEN treatment demonstrated a reduced number of tail flicks, back leg forward and strains (P < 0.05; Table 1). Additionally, OPEN sows displayed reduced nosing of crate fixtures and increased number of postural changes (P < 0.001; Table 1). No differences in bar-biting/champing or plasma cortisol concentration at any time were observed (P > 0.05).

Table 1.  The number of pain related behaviours observed during farrowing for animals housed in OPEN or CLOSED pens

We have shown that allowing the sow greater movement leading up to and during parturition resulted in a reduced incidence of behaviours indicative of pain. These findings suggest that confinement may result in a reduction in the level of parturition – induced hypoalgesia, but further more objective measures of pain are required to support this notion.