Evidence suggests that piglets do encounter acute pain from the castration process. However, little is known about the persistence of pain after the first few hours following the procedure.

So, a group of researchers looked, behaviorally and physiologically, for signs of pain persistence for five days following castration. Their findings were reported in the Applied Animal Behaviour Science 82 (3): 201-218, 2003 (Hay, M.; Vulin, A.; Genin, S.; Sales, P.; Prunier, A.)

Five-day-old piglets were castrated, sham-castrated or left un-disturbed in their pen. Treatments were applied within litters.

The researchers used two methods for behavioral observations: 1) scan sampling, using a detailed ethogram during the daytime and continuous observations during the night. 2) Physiological responses were monitored by measuring corticosteroids and catecholamines (stress-related hormones) in the animal’s urine.

Behavioral observations performed for five days after castration showed that castrated piglets spent less time at the sow’s udder (massaging and suckling) and were less active while awake during the first 2.5 hours following castration compared to their non-castrated littermates.

Castrated piglets tended to walk more throughout the experiment. They showed significantly more pain/castration related behaviors – prostration, stiffness and trembling – during the first hours following treatment. Also, for at least two days following castration, those piglets scratched their rumps and wagged their tails more – both signs of irritation. Throughout the experiment, they huddled up more than other piglets.

Concerning tail wagging, the difference between the two groups tended to be significant four days after castration. Scratching the rump peaked 24 hours after castration but was still present on the fourth night following castration. Castrated piglets displayed less sociability – they were more frequently found isolated during the first 2.5 hours after the process, and were more often desynchronized the afternoon following castration and 24 hours later.

Castration had no clear effect on urinary corticosteroids and catecholamines. Growth performance did not differ between the two groups.

The researchers conclude that overall, these results confirm that castration induces pain, and that behavioral responses are exacerbated during the first few hours following the process. However, many behavioral alterations persist beyond 24 hours, some of which continue for four days after castration. This suggests that piglets suffer from pain for more than a few hours following the process. They say it emphasizes the need to develop analgesic protocols or alternative methods to castration.