Piglets' acute responses to procaine-based local anesthetic injection and surgical castration: Effects of two volumes of anesthetic

Abstract

Surgical castration of piglets is painful, but practiced routinely in commercial pig production. Procaine-based local anesthetics are used to mitigate piglet pain during castration in some countries. Yet, effects of the volume of anesthetic injected remain under-studied. The volume of drug administered may modulate the pain mitigating effect via variation in intra-testicular pressure at injection, potentially leading to pain or discomfort, as well as variation in the dose of active ingredient administered. The present study investigated the effects of injection with two volumes of a procaine-based local anesthetic, 0.3 vs. 0.5 mL per testis, on acute responses of 3–4 day old piglets. A total of 290 piglets were divided into 5 treatment groups: castration without anesthesia, castration after intra-testicular injection of 0.5 or 0.3 mL of drug per testis, and sham handling with one or two stays in a castration bench. Acute responses to drug injection, castration and sham handling were evaluated based on quantification of intra-procedural vocalizations and foreleg movements, as well as saliva cortisol concentrations before and after castration. Regardless of the volume, injection of anesthetic as well as castration led to significantly stronger responses than sham handling. Responses to the two drug volumes did not differ significantly, and responses to castration following injection of 0.3 mL did not differ from piglets castrated without anesthesia. All treatments, including sham handling, led to a significant increase in saliva cortisol, and no difference was found between anesthesia treatments and sham handling. Overall, the results suggested that injection of 0.5 mL led to better pain mitigation at castration compared to injection of 0.3 mL, but even when the local anesthetic was used, the combined procedures of injection and castration led to intra-procedural signs of pain and stress.

Piglets' acute responses to local anesthetic injection and surgical castration: Effects of the injection method and interval between injection and castration

“…Our results showed that, overall, administration of the procaine-based local anesthetic reduced the acute responses of piglets to castration, as measured by the number of foreleg movements interpreted as resistance and vocalization characteristics (including number, duration, and intensity of calls), as compared to piglets castrated without anesthesia. These results are based on quantitative recording of resistance movements and automatic detection and characterization of vocal parameters developed in the study, and are in line with previous results ( 11 , 14 , 23 , 27 ). Thus, these methods seem to be able to detect subtle differences in piglets' acute responses to early-life interventions.…”

“…Duration of each procedure was recorded. All vocal files were analyzed in Raven Pro 1.6 bioacoustics analysis software (Cornell Lab of Ornithology, Ithaca, New York, USA) using the band limited energy detector function, as described in Coutant et al ( 27 ). This function allowed each intra-procedural call to be automatically detected based on a pre-set of parameters (data in Supplementary Text S1 ), and characterized in terms of number, duration, energy, and entropy.…”

“…This distance allowed a full picture of the piglets' front legs. Resistance movements were quantified using a novel method developed in Coutant et al ( 27 ). Video clips were observed at low speed (5 FPS) to detect four types of movements: flexion, extension, kick, and blow ( Table 3 ; Figure 2 ).…”

“…For changes in saliva cortisol in response to the procedures, one sample per piglet was collected on average 17 (±9) min after castration and again approximately 6 h after castration (5 h 47 min ±26 min). Saliva samples were performed using a novel method recently used in Coutant et al ( 27 ); a cotton swab (Salivette ® , Sarstedt, Aktiengesellschaft & Co., Numbrecht, Germany) was cut in pieces (approx. 2.0 × 0.5 cm), soaked in concentrated apple juice (nectar from concentrated juice, min 60%, Rynkeby Foods A/S, Ringe, Denmark) for 1 h, and dried in an electric oven at 60°C for 5 h. A pilot study revealed an increase in saliva production with this method compared to the use of a non-pre-soaked piece of cotton.…”

“…Textbooks reviewing lidocaine and procaine report differences in terms of onset of action, efficacy and potency ( 24 – 26 ). In addition, recent studies suggested unsatisfactory pain mitigation of procaine administered alone before surgical castration of 3–7 day old piglets ( 12 , 22 , 27 ).…”