Effect of surgical castration on the behavioural and acute phase responses of 5-day-old piglets

Pain and discomfort provoked by surgical castration of male pigs causes behavioural alterations that are particularly evident in the immediate days following this procedure. Less information is available in relation to whether the physiological consequences of surgical castration also persist with time. The objective of this study was to assess the behavioural response to this procedure; and evaluate its effects on levels of the pro-inflammatory cytokines tumor necrosis factor-alpha (TNF-α) and interleukin-1beta (IL-1β), as well as cortisol [Exp. 1]; and the acute phase proteins C-reactive protein (CRP), serum amyloid A (SAA) and haptoglobin (Hp) [Exp. 2]. Forty male piglets were used in each experiment. At 5 days-of-age, pigs were randomly assigned to undergo surgical castration or to being handled identically but not castrated (treatments were imposed in the morning period). Behaviour was assessed by scan sampling every 3 min for 3 h in the afternoon period on the day of castration [Exp. 1]; and for intervals of 2.5 h on the day of castration (morning and afternoon periods) and 2 h-intervals on three consecutive days thereafter (afternoon period) [Exp. 2]. Pigs were assigned to one of five sampling times, where blood was collected by venipuncture before (0 h), 1, 2, 3 or 4 h [Exp. 1] and 0, 12, 24, 48 or 72 h after treatments [Exp. 2]. Castration provoked specific pain-related behaviours (P < 0.001) throughout the duration of both experiments, but particularly immediately after castration [Exp. 2]. These included behaviour such as huddling up, spasms and trembling. Castrated pigs walked less (P < 0.05) and avoided dog-sitting postures (P < 0.01). In Exp. 1, castrates tended to spend more time at the udder (P < 0.1) and in contact with the sow (P < 0.05). In Exp. 2, castrated pigs spent more time alone (i.e. not in contact with sow or siblings) (P < 0.05). Castrated pigs tended to be more isolated and desynchronised (P < 0.1). Castration had no effect on plasma levels of TNF-α, IL-1β, CRP, SAA and Hp (P > 0.1). Castrated piglets tended to have higher cortisol levels than handled pigs (P < 0.1). Hence, behavioural observations were useful for evaluating the consequences of surgical castration on the welfare of pigs, indicating that animals undergoing this surgical procedure experience pain and discomfort that is persistent for up to 4 days. However, pro-inflammatory cytokines and acute phase proteins did not provide relevant information on the physiological consequences of this husbandry practice.