Effect of local anaesthesia and/or analgesia on pain responses induced by piglet castration

Abstract

Background: Surgical castration in male piglets is painful and methods that reduce this pain are requested. This study evaluated the effect of local anaesthesia and analgesia on vocal, physiological and behavioural responses during and after castration. A second purpose was to evaluate if herdsmen can effectively administer anaesthesia.

Methods: Four male piglets in each of 141 litters in five herds were randomly assigned to one of four treatments: castration without local anaesthesia or analgesia (C, controls), analgesia (M, meloxicam), local anaesthesia (L, lidocaine), or both local anaesthesia and analgesia (LM). Lidocaine (L, LM) was injected at least three minutes before castration and meloxicam (M, LM) was injected after castration. During castration, vocalisation was measured and resistance movements judged. Behaviour observations were carried out on the castration day and the following day. The day after castration, castration wounds were ranked, ear and skin temperature was measured, and blood samples were collected for analysis of acute phase protein Serum Amyloid A concentration (SAA). Piglets were weighed on the castration day and at three weeks of age. Sickness treatments and mortality were recorded until three weeks of age.

Results: Piglets castrated with lidocaine produced calls with lower intensity (p < 0.001) and less resistance movements (p < 0.001) during castration. Piglets that were given meloxicam displayed less pain-related behaviour (huddled up, spasms, rump-scratching, stiffness and prostrated) on both the castration day (p = 0.06, n.s.) and the following day (p = 0.02). Controls had less swollen wounds compared to piglets assigned to treatments M, L and LM (p < 0.001). The proportion of piglets with high SAA concentration (over threshold values 200, 400 mg/l) was higher (p = 0.005; p = 0.05) for C + L compared to M + LM. Ear temperature was higher (p < 0.01) for controls compared to L and LM. There were no significant treatment effects for skin temperature, weight gain, sickness treatments or mortality.

Conclusions: The study concludes that lidocaine reduced pain during castration and that meloxicam reduced pain after castration. The study also concludes that the herdsmen were able to administer local anaesthesia effectively.

Figure 1

Effect of treatment on call intensity. Mean value and SD for call intensity (dB(A)) for the treatments C, M, L and LM. Piglets castrated with lidocaine (L and LM) produced calls with significantly (p < 0.001) lower intensity than piglets castrated without lidocaine (C and M). Means with different letters indicate significant differences (p < 0.05).

Figure 2

Effect of treatment on call intensity in the five herds. Mean value for call intensity (dB(A)) for the treatments C, M, L and LM, per herd. There were no significant interactions between treatment and herd.

Figure 3

Ranking of resistance movements during castration. Piglets castrated with lidocaine (L and LM) showed significantly (p < 0.001) less resistance movements than piglets castrated without lidocaine (C and M).

Figure 4

Ranking of castration wounds swelling the day after castration. Controls (C) had significantly less swollen wounds compared with treatments M, L and LM (p < 0.001).