Rearing pigs with play opportunities: viral load and clinical, behavioural, performance, and immune data

Positive emotions can reduce disease susceptibility during
infectious challenges in humans, and emerging evidence suggests
similar effects in farm animals. Because play behaviour may
support a positive emotional state in pigs, this study
investigates whether rearing pigs with regular intermittent play
opportunities enhances disease resilience when challenged with
porcine reproductive and respiratory syndrome virus (PRRSV).
Litters were assigned to either play (PLY; n = 5 L) or control
(CON; n = 4 L) treatments at birth. In PLY, play was promoted
with extra space and enrichment items for three hours daily from
five days of age (doa). At weaning (25 ± 2 doa; mean ± SD), 28 pigs
(14/treatment) were selected for a disease challenge, based on weight,
sex, and sow. The pigs were transported to a disease containment
facility and at 43 ± 2 doa (day 0 post-inoculation, DPI)
inoculated with PRRSV. Skin lesions, blood, rectal temperature,
clinical signs, body weight, and behaviour were collected pre-
and post-inoculation. Play opportunities for PLY continued every other
day until euthanasia of all pigs at 65 ± 2 doa (22 DPI). PLY pigs
exhibited fewer skin lesions following transport and throughout
the infection compared to CON. Although the viral load did not
differ between treatments, PLY pigs had a lower probability of
experiencing moderate and severe respiratory distress, with
a shorter duration. PLY also performed better throughout the
infection, showing higher ADG and greater feed efficiency. The
immune response differed as well. PLY pigs had fewer monocytes on
8 DPI than CON, with levels returning to baseline by 21 DPI,
whereas CON levels exceeded baseline. Regardless of day of infection,
lymphocyte counts tended to be lower in PLY than in CON, and white blood
cells and neutrophils were also lower, but only in slow-growing pigs. PLY
pigs continued to play during the infection, demonstrating less
sickness behaviour and emphasizing the rewarding properties of
play. Results suggest that PLY pigs were less affected by PRRSV
and developed increased resilience to PRRSV compared to CON.
This study demonstrates that rearing pigs in an environment
supporting positive experiences through provision of play
opportunities can enhance resilience against common modern
production challenges, underscoring the value of positive welfare
in intensive pig farming.