Edited by: T. Bas Rodenburg, Utrecht University, Netherlands
Reviewed by: Regula Bettschart, University of Zurich, Switzerland; Nancy De Briyne, Federation of Veterinarians of Europe, Belgium
This article was submitted to Animal Behavior and Welfare, a section of the journal Frontiers in Veterinary Science
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Although applied in some countries, efficacy of local anesthetics based on procaine to mitigate acute responses to piglet castration remains questioned. This paper presents results from a factorial study examining the effects of two methods of injection of a procaine-based drug (intra-funicular, IF, vs. intra-testicular, IT), and four intervals between drug injection and castration (2.5, 5, 10, and 30 min) on acute responses of 3–4 day old piglets. The study involved 597 male piglets, and 13 treatments: surgical castration without anesthesia (CC), local anesthesia followed by castration involving all combinations of injection method and interval, and sham handling separated by the same four intervals (SH). Responses of piglets to drug injection, castration and sham handling were evaluated based on quantification of intra-procedural vocalizations and leg movements, as well as saliva cortisol concentration in samples taken before and after castration. No differences were found between IF and the simpler IT injection method. Intervals of 2.5 or 30 min led to stronger piglet responses than the other intervals. Overall, treatments involving anesthesia led to significantly stronger responses than sham handling, during both injection and castration. All treatments, even sham handling, led to a significant increase in saliva cortisol, with no differences between anesthesia treatments and controls. Based on these results, castration 5–10 min after intra-testicular injection of procaine seems to be preferable as compared to the other treatments tested. However, piglets still showed measurable signs of pain and stress during both injection and castration, while handling alone (including the use of a castration bench) triggered a noticeable stress response. In light of these findings, the overall benefit of the procedure in terms of piglet welfare remains arguable.
Surgical castration is a routine practice that involves millions of pigs yearly in the EU and other global regions. The procedure, consisting of the removal of the male piglets' testes
In Denmark, the fourth largest producer of pigs in Europe (
Yet, most studies investigating the efficacy of local anesthesia to mitigate piglet pain have been carried out in laboratory-like conditions, involving procedures performed by skilled veterinarians [e.g., (
While the efficacy of local anesthesia administered prior to piglet castration has been mostly reported in studies using lidocaine, procaine is the active ingredient most frequently used as anesthetic for pig castration in the EU (
Irrespectively of the drug used, knowledge on the welfare impact of castration with prior administration of local anesthetics remains limited, as only few studies have reported piglets' response to the injection itself. As reviewed by Kongsted et al. (
The aim of the present study was to compare the effect of two methods of injection of procaine as a local anesthetic and four time intervals between injection and castration on piglets' responses to injection and castration in field trial conditions resembling commercial practice. Acute responses were evaluated based on vocalizations and number of leg movements, interpreted as resistance, during injection and castration, as well as saliva cortisol concentrations before and after surgical castration.
The experiment was carried out between July and October 2020 and was conducted in a Danish conventional sow herd with approximately 1,300 sows giving birth to (Landrace × Yorkshire) × Duroc crossbred piglets. Sows were loose-housed in farrowing pens measuring 3.1 × 2.8 m, set as a crate in the first week post-farrowing, i.e., during the experiment.
Trials were conducted 2 days per week, corresponding to the routine days of castration at the farm. Earlier in the week, litters reaching 3 to 4 days of age on the weekday of experimentation (with day 0 defined as the day of birth of the last piglet in a litter), and counting at least six males, were clinically assessed, and male piglets selected. All selected piglets were clinically healthy and free of overt anatomical malformations. Piglets weighting < 0.9 or >2.3 kg on the day of selection were not included in the study, due to a risk of improper fit in the castration bench during testing. Each of six male piglets selected within a litter was randomly assigned to one of 13 treatment groups (
Description of the 13 treatment groups involved in the study.
IF | IF | IF | IF | IT | IT | IT | IT | – | SH | SH | SH | SH | |
2.5 | 5 | 10 | 30 | 2.5 | 5 | 10 | 30 | – | 2.5 | 5 | 10 | 30 | |
50 | 50 | 50 | 49 | 50 | 49 | 50 | 49 | 50 | 50 | 25 | 25 | 50 |
Apart from CC (control castrated), all treatments were a combination of a method of injection (IM): IF, intra-funicular injection; IT, intra-testicular injection; SH, sham handling; and time interval between injection and castration (TI, min): 02, 2.5 min; 05, 5 min; 10, 10 min; 30, 30 min. N, number of piglets tested per treatment.
All piglets were identified by a number written on their back using a food-safe marker. Experimental piglets were allowed to be cross-fostered in the first days of life, but could not be moved from their litter after selection. Cross-fostering of non-experimental littermates was permitted up to the morning prior to castration. The piglets were administered a suspension of 45 mg toltrazuril and 200 mg gleptoferron (Forceris™, 1.5 mL, Ceva Animal Health A/S, Libourne, France) on day 1 after farrowing. The experimental piglets were not ear tagged, tail docked, or teeth clipped before castration. In order to avoid confounding of the results on the efficacy of the local anesthetic, piglets were administered an NSAID (intramuscular injection of 1.5 mg meloxicam; Melovem, 0.3 mL, Dopharma, The Netherlands) as analgesic after completion of the data collection and within 24 h after castration.
On the day of castration, experimental piglets were weighed. Saliva samples were taken approximately 35 to 40 min before bringing the piglets to the testing area, a calm room outside the farrowing room. All experimental piglets plus one extra littermate selected at random were transported together in a plastic box (size: 71.5 × 53.0 × 39.5 cm) layered with straw, and placed underneath a heat lamp (averaging 20°C, ranging from 15 to 25°C at recipients) upon arrival in the testing area. Piglets were injected, castrated or sham handled one by one, respecting a randomized testing order, and following a predefined schedule ensuring that the experimental intervals between procedures were respected. During all procedures, piglets were fixated while lying on their back, in a commercially available castration bench (Unitron A/S, Kolding, Denmark). For the experimental purpose, the bench was modified to enable larger amplitudes of front leg movements, and more natural opening of the mouth during vocalizing. To further ensure a proper fit in the bench, considering the variation in piglets' body size, a soft material (5-mm yoga matt; Figure in
In-between procedures, piglets were returned to the heated box with their littermates. Immediately after castration or last sham handling, piglets were individually subjected to complementary testing not reported in the present paper, and brought back to the sow in the farrowing pen. On average 17 min after castration or last sham handling, a second saliva sample was taken in the farrowing unit. Later in the afternoon, approximately 6 h after castration, a last saliva sample was taken for cortisol determination.
In accordance with the clinical trial permit (described below), piglets were closely monitored for drug-related side effects up to 72 h after anesthetic injection and castration.
Two experimenters were present in the testing area: an experimenter performing the procedures, and an experimenter starting and stopping the recordings. These two were not blinded to the experimental treatments. All other experimenters, selecting the piglets, sampling them, recording the data and creating the datasets were blinded until the start of the statistical analysis.
A total of 597 piglets were assigned to one of thirteen treatments (
All surgical and injection procedures were performed by the same experimenter, an experienced farm staff from Aarhus University trained in accordance with standards from the DVFA (
The anesthetic used in the study was a procaine hydrochloride 2% solution (Procamidor® Vet., 20 mg/mL, Richter Pharma AG, Wels, Austria). The product was administered using an automatic syringe (Prima Tech® 0.5 mL in 0.1 mL increments) with a 25G needle for the intra-funicular injection (0.5 × 16 mm, BD Microlance™ 3, BD, New Jersey, USA). For the intra-testicular injection, in order to get the shortest needle length possible, a 26G needle (0.45 × 12 mm, Sterican® Insulin needle, B Braun Medical SA, Barcelona, Spain) was used, together with a 5 mm plastic stopper. Needles were changed between each piglet.
Piglets were fixated in dorsal recumbency position in the castration bench, and testes were fixed carefully in the distal end of the scrotum. The scrotum area was not disinfected prior to anesthetic injection nor castration. The right testis was fixed caudally between the thumb and index finger of the experimenter, applying a steady but low pressure during the fixation. For the intra-funicular injection, the needle was inserted at a 45-degree angle pointing in dorsal direction and a 10-degree angle pointing in lateral direction from a caudocranial view (
The two methods of injection of the local anesthetic.
After fixation in the castration bench, a disposable scalpel (Scalpel no. 24, carbon steel sterile blade, Swann-Morton, Sheffield, England) was used to perform an incision (approximately 1 cm) through the scrotal skin and spermatic fasciae. The right testis was then gently pressed between the index and the thumb of the experimenter until fully outside of the scrotum. The testis was then carefully lifted vertically, and the spermatic cord cut a few millimeters below the testis using the scalpel. The incision was repeated on the left testis. A new scalpel was used for each piglet. A video of the procedure is available in
Piglets were fixated in the castration bench, as previously described, for a duration of approximately 25 s (corresponding to the average duration of the procedures of local anesthesia and castration as assessed in a pilot study), during which they did not experience any tissue damage nor physical stimulation of the groin area.
The study was performed in compliance with the EU Directive 2010/63/EU for animal experiments, the Ministry of Food, Agriculture and Fisheries, and The Danish Veterinary and Food Administration under act 474 of 15. May 2014 and executive order 2028 of 14. December 2020. The experiment was approved as a clinical trial by the Danish Medical Agency (reference number 2020061784). All procedures were ethically evaluated and approved by the Danish Animal Experiments Inspectorate (Approval number 2019-15-0201-00263).
The vocal responses of the piglets were recorded during each procedure, using a microphone (Sennheiser E614, Sennheiser Wennebostel, Germany) fixed 30 cm ahead of the piglet's snout, at the level of the head of the piglet. The microphone was connected to an amplifier (Audiobox USB® 96, PreSonus, Louisiana, USA) connected to a computer, from which recordings were manually started and stopped upon piglet's placement and removal from the castration bench. 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. (
Description of the vocal parameters analyzed for each piglet during injection of local anesthetic, castration, or sham handling, all performed while the piglet was in the castration bench.
Call proportion | Proportion of time spent vocalizing during the procedure, calculated as call duration /procedure duration. |
Call per second (s−1) | Number of calls per s of the procedure |
Mean call duration (s) | Average duration of a call during the procedure, calculated as sum of call durations/number of calls. |
Mean energy (dB) | Average energy, calculated as an average of the energy of each call during the procedure. |
Max energy (dB) | Maximum value of energy recorded for all calls during the procedure. |
Max power (dB) | The maximum power recorded for all calls during the procedure, relative to the specific recording set-up. |
Aggregated entropy (kilobits) | Aggregated disorder for the procedure obtained by analyzing the energy distribution within each call. Higher entropy values correspond to greater disorder in the sound whereas a pure tone would have zero entropy ( |
Max entropy (kilobits) | Highest value of disorder recorded for all calls during the procedure. |
Four distinct types of front leg movements, interpreted as resistance movements, were recorded during each procedure using a camera (GoPro HERO7 Black, GoPro, San Mateo, California, USA; 60 frames per sec, FPS) placed on a stand 30 cm to the right of the castration bench, approximately 50 cm above the bench. This distance allowed a full picture of the piglets' front legs. Resistance movements were quantified using a novel method developed in Coutant et al. (
Description of the leg resistance movements recorded during injection of local anesthetic, castration, or sham handling, all performed while the piglet was in the castration bench.
Flexion | Piglet vertically bends his front leg, provoking a flexion of the elbow of at least 90 degrees. |
Extension | Piglet fully extends his front leg while lowering the head in the bench. May be accompanied by trembling of the leg and/or by a subtle lift of the piglet's back. |
Kick | Piglet front leg performs a sudden upwards movement, changing from a flexion to a tense upwards position. |
Blow | Piglet suddenly draws back his front leg forwards or backwards for at least half a bench length, from a normal upright position to an extended position, with little or no flexion of the elbow. |
Leg blocked | Piglet's front leg is blocked in the bench cone, preventing movement. |
Each leg was scored separately.
Visual representation of the four leg resistance movements recorded during injection of local anesthetic, castration, or sham handling while in the castration bench. F, Flexion; K, Kick; E, Extension; B, Blow. The visualizations only show the leg movements, see further description of the categories in
For baseline, one saliva sample per piglet was collected in the home pen on average 35 (±14; SD) min before the first procedure. 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. (
Three piglets were removed from the analysis: two piglets due to experimental issues during the procedures, and one due to cryptorchidism (only one testis descended) discovered during injection of the local anesthetic. In addition, for two piglets, insufficient amounts of saliva rendered cortisol analysis impossible, and eight piglets were excluded from the resistance movement analysis due to technical issues with the recording of the videos (five for injection and three for castration). Malfunctioning and technical issues of the vocalization recording set-up resulted in 168 missing files for anesthesia and 182 missing files for castration, leaving valid vocalization data from 376 piglets for anesthesia and 412 piglets for castration.
Vocalizations and resistance movements were analyzed separately for local anesthesia and castration. During the injection of the local anesthetic, time interval had not yet any bearing, and thus for the first procedure only three treatments were relevant: injection by intra-funicular method (IF), injection by intra-testicular method (IT), and sham handling (SH).
The vocalization parameters (
The counts of each type of resistance movements were summed per piglet during each procedure (
Changes in saliva cortisol in response to the procedures were log transformed and analyzed in a mixed model with treatment, sampling point (early - late) and their interaction as fixed effects of main interest, and weight, age, time of sampling (decimal h, range: 7.82–20.50), and baseline cortisol concentration (range: 2,001–48,570 pg/mL) as covariates, with sample point as a repeated measure, and litter as random effect.
For all outcomes, initial models were reduced by stepwise removal of fixed effects at
In case the final model showed significant effect of the treatments (
Vocal responses of piglets during administration of the local anesthetic were affected by the treatments. A significant difference was observed in 6 out of 8 indicators (
Averages (± SE) of vocal parameters recorded during injection of the local anesthetic.
Call proportion | 0.63 ± 0.01 |
0.64 ± 0.01 |
0.47 ± 0.02 |
F2, 314 = 29.4 | < 0.001 |
Call per second (s−1) | 0.90 ± 0.02 |
0.88 ± 0.02 |
0.66 ± 0.03 |
F2, 314 = 39.3 | < 0.001 |
Mean call duration (s) | 0.75 ± 0.03 | 0.76 ± 0.02 | 0.72 ± 0.03 | F2, 311 = 1.6 | 0.201 |
Mean energy (dB) | 84.80 ± 9.17 |
85.13 ± 9.12 |
46.41 ± 10.10 |
F2, 310 = 5.6 | 0.004 |
Max energy (dB) | 319.98 ± 8.54 |
318.51 ± 7.94 |
288.21 ± 10.46 |
F2, 311 = 3.2 | 0.041 |
Max power (dB) | −14.24 ± 0.74 |
−14.40 ± 0.67 |
−17.06 ± 0.89 |
F2, 311 = 4.3 | 0.015 |
Agg entropy (kilobits) | 130.54 ± 3.27 |
122.08 ± 2.85 |
108.82 ± 4.40 |
F2, 330 = 33.8 | < 0.001 |
Max entropy (kilobits) | 5.94 ± 0.01 | 5.91 ± 0.01 | 5.93 ± 0.02 | F2, 312 = 1.1 | 0.340 |
At castration, all vocalization indicators showed significant treatment differences (
Averages (±SE) of vocal parameters recorded during castration.
Call proportion | 2.5 min | 0.61 ± 0.03 |
0.59 ± 0.03 |
0.43 ± 0.04 |
F12, 370 = 6.8 | < 0.001 |
5 min | 0.59 ± 0.03 |
0.60 ± 0.03 |
0.51 ± 0.07 |
|||
10 min | 0.55 ± 0.03 |
0.58 ± 0.02 |
0.44 ± 0.05 |
|||
30 min | 0.60 ± 0.03 |
0.66 ± 0.03 |
0.43 ± 0.04 |
|||
CC | 0.72 ± 0.02 |
0.72 ± 0.02 |
0.72 ± 0.02 |
|||
Call per second | 2.5 min | 0.87 ± 0.05 |
0.87 ± 0.05 |
0.68 ± 0.05 |
F12, 363 = 6.7 | < 0.001 |
5 min | 0.91 ± 0.04 |
0.89 ± 0.05 |
0.63 ± 0.07 |
|||
10 min | 0.95 ± 0.04 |
0.94 ± 0.03 |
0.69 ± 0.07 |
|||
30 min | 0.94 ± 0.04 |
0.87 ± 0.04 |
0.64 ± 0.05 |
|||
CC | 0.92 ± 0.04 | 0.92 ± 0.04 | 0.92 ± 0.04 |
|||
Mean call duration (s) | 2.5 min | 0.75 ± 0.05 |
0.70 ± 0.05 |
0.63 ± 0.04 |
F12, 364 = 2.4 | 0.006 |
5 min | 0.70 ± 0.05 |
0.70 ± 0.05 |
0.81 ± 0.11 |
|||
10 min | 0.60 ± 0.04 |
0.62 ± 0.03 |
0.67 ± 0.08 |
|||
30 min | 0.68 ± 0.04 |
0.81 ± 0.05 |
0.68 ± 0.05 |
|||
CC | 0.82 ± 0.04 |
0.82 ± 0.04 |
0.82 ± 0.04 |
|||
Mean energy (dB) | 2.5 min | 34.58 ± 15.75 |
52.37 ± 16.6 |
0.15 ± 15.52 |
F12, 358 = 4.8 | < 0.001 |
5 min | 25.88 ± 16.43 |
29.59 ± 18.05 |
42.88 ± 29.40 |
|||
10 min | 19.28 ± 19.23 |
12.93 ± 11.93 |
−2.34 ± 21.16 |
|||
30 min | 50.27 ± 18.81 |
59.10 ± 18.68 |
6.74 ± 15.40 |
|||
CC | 131.20 ± 16.32 |
131.20 ± 16.32 |
131.20 ± 16.32 |
|||
Max energy (dB) | 2.5 min | 299.20 ± 16.71 |
302.53 ± 15.36 |
244.89 ± 18.90 |
F12, 359 = 3.5 | < 0.001 |
5 min | 273.55 ± 18.78 |
285.58 ± 19.65 |
271.39 ± 24.91 |
|||
10 min | 265.70 ± 20.45 |
268.42 ± 17.46 |
250.20 ± 26.68 |
|||
30 min | 292.07 ± 18.28 |
302.51 ± 14.16 |
243.05 ± 18.59 |
|||
CC | 349.24 ± 11.32 |
349.24 ± 11.32 |
349.24 ± 11.32 |
|||
Max power (dB) | 2.5 min | −15.22 ± 1.52 |
−15.20 ± 1.34 |
−20.20 ± 1.79 |
F12, 359 = 3.2 | 0.002 |
5 min | −18.42 ± 1.73 |
−17.44 ± 1.73 |
−18.65 ± 2.02 |
|||
10 min | −17.87 ± 1.64 |
−19.36 ± 1.59 |
−20.52 ± 2.20 |
|||
30 min | −15.92 ± 1.54 |
−15.92 ± 1.15 |
−20.39 ± 1.54 |
|||
CC | −11.83 ± 1.04 |
−11.83 ± 1.04 |
−11.83 ± 1.04 |
|||
Agg. entropy (kilobits) | 2.5 min | 136.12 ± 7.23 |
136.52 ± 10.25 |
110.08 ± 9.03 |
F12, 363 = 6.3 | 0.001 |
5 min | 144.72 ± 12.55 |
138.54 ± 7.39 |
100.73 ± 11.52 |
|||
10 min | 149.04 ± 7.25 |
141.56 ± 6.84 |
103.88 ± 9.52 |
|||
30 min | 149.11 ± 7.48 |
133.58 ± 5.92 |
108.61 ± 9.11 |
|||
CC | 148.54 ± 6.23 | 148.54 ± 6.23 | 148.54 ± 6.23 |
|||
Max entropy (kilobits) | 2.5 min | 5.97 ± 0.03 | 5.96 ± 0.03 | 5.93 ± 0.02 | F12, 361 = 1.7 | 0.067 |
5 min | 6.00 ± 0.03 | 6.00 ± 0.03 | 5.97 ± 0.03 | |||
10 min | 5.99 ± 0.04 | 5.99 ± 0.04 | 5.98 ± 0.04 | |||
30 min | 5.96 ± 0.03 | 5.98 ± 0.03 | 6.00 ± 0.02 | |||
CC | 5.89 ± 0.03 | 5.89 ± 0.03 | 5.89 ± 0.03 |
1, 2Different numbers within a row indicate significant differences between injection methods within intervals for the given parameter.
Piglets' leg movements during injection of the local anesthetic differed significantly among treatments, with greater levels of movements observed in IF and IT than in SH. The leg movements observed during intra-testicular and intra-funicular injections did not differ significantly, although piglets injected by the intra-funicular method displayed an average of 17.6% more leg movements than piglets injected by the intra-testicular method. At castration, the number of resistance movements differed significantly among treatments (
Averages (±SE) of leg resistance movements recorded during castration.
28.44 ± 1.26 |
23.85 ± 1.02 |
14.32 ± 1.08 |
< 0.001 | |||
24.62 ± 2.13 |
30.26 ± 2.71 |
13.96 ± 1.77 |
< 0.001 | |||
24.23 ± 2.58 |
26.49 ± 2.63 |
11.08 ± 2.58 |
||||
30.22 ± 3.85 |
26.96 ± 2.65 |
16.08 ± 3.34 |
||||
29.51 ± 2.41 |
30.96 ± 3.00 |
15.69 ± 2.01 |
||||
41.06 ± 2.72 |
41.06 ± 2.72 |
41.06 ± 2.72 |
At anesthesia (Anaest.),
As expected, baseline cortisol concentrations from samples obtained 35–40 min before the procedures did not differ significantly among treatments (approx. 9,700 pg/mL, F12, 503 = 0.8,
The interaction between treatments and timing of sampling was not significant (F12, 1044 = 1.56,
Considering the significant difference between cortisol concentrations measured at 17 min and 6 h post-procedure, two separate analyses were performed. At 17 min, treatment groups differed in cortisol concentration (
Averages (±SE) of saliva cortisol concentrations (pg/mL) sampled at 17 min post-castration.
2.5 min | 16,958 ± 1,100 |
17,518 ± 1,277 |
18,589 ± 1,255 |
F12, 518 = 2.5 | 0.003 |
5 min | 16,367 ± 1,196 |
16,291 ± 816 |
18,742 ± 1,750 |
||
10 min | 19,132 ± 1,289 |
19,605 ± 1,482 |
13,687 ± 1,289 |
||
30 min | 19,713 ± 1,325 |
17,207 ± 936 |
15,842 ± 1,053 |
||
CC | 15,057 ± 858 |
15,057 ± 858 |
15,057 ± 858 |
1, 2Different numbers within a row indicate significant differences between methods within intervals.
At 6 h post-procedure, piglets' cortisol responses did not differ significantly among treatments (F12, 523 = 0.7, P=0.721, Table in
We aimed in this study to assess piglets' acute responses to two methods of injection of a local anesthetic, and surgical castration following four different time intervals after the injection. Acute responses were evaluated based on piglet vocalizations, leg movements interpreted as resistance, and saliva cortisol concentrations in samples obtained at two time points after castration (at approximately 17 min and approximately 6 h). Results showed no significant difference between the two injection methods. Greater acute responses were observed during castration performed 2.5 and 30 min compared to 5 or 10 min after the injections. Saliva cortisol concentrations in samples obtained from piglets castrated after injection with the local anesthetic did not differ significantly from those of piglets castrated without any anesthesia or sham handled. Below, these findings are discussed in terms of methodology and in relation to animal welfare.
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 (
Saliva-sampling of 3–4 day old piglets is difficult as they produce relatively low amounts of saliva, and display less spontaneous chewing on cotton swabs during sampling than older piglets being experienced with solid feed intake. The present technique, developed in Coutant et al. (
The present findings on saliva cortisol are, however, not in line with previous studies showing a lowered cortisol response to castration in piglets administered a local anesthetic prior to castration compared to piglets castrated without anesthesia (
In relation to the interpretation of the cortisol results, concern has been raised for years regarding the usefulness of cortisol and other physiological indicators to inform about the affective component of pain, as these indicators may be more related to the level of arousal induced by the procedure (
To the best of our knowledge, only one other study has investigated the efficacy of a local anesthetic as pain mitigating when administered in practice by farmers. The authors concluded that herdsmen were able to effectively inject a local anesthetic intra-testicularly, resulting in comparable efficacy of anesthesia as reported in other studies involving trained veterinarians (
Our study did not show a significant difference in acute responses of piglets exposed to the intra-testicular vs. intra-funicular injection methods. This result is in line with a previous study performed in piglets under general anesthesia, and also comparing the two methods (
The effect of interval between injection of local anesthetic and castration is poorly investigated in the literature, and seem to only have been included in one study by Courboulay et al. (
Overall, our results showed that injection of procaine as a local anesthetic allows some mitigation of piglets' acute responses to castration, but leads to significant responses during the injection of the anesthetic. Piglets in the present study did not receive any analgesic [as is mandatory in Denmark (
In the future, the use of local anesthetics prior to piglet castration in Europe may be further improved by the approval of other local anesthetics than procaine, such as lidocaine, which may have an increased efficacy at castration compared to procaine (
In conclusion, while our study provided further insights into the administration of a procaine-based local anesthetic prior to piglet castration, and has provided results allowing a refinement of the procedure, we cannot oversee that castration with local anesthesia remains a welfare concern. This concern has been raised previously [e.g., (
The original contributions presented in the study are included in the article/
The animal study was reviewed and approved by the Danish Animal Experiments Inspectorate. Written informed consent was obtained from the owners for the participation of their animals in this study.
The study was designed by the project group involving MH, JM, MC, and MK with advice from LF. MK developed the anesthesia injections and trained the herdsman. MC was in charge of the data collection, data processing, and data analysis with supervision from JM, LF, and MH. LF performed the sample size calculations. MC drafted the manuscript. All authors contributed to the article and approved the submitted version.
This study was commissioned and funded by the Danish Veterinary and Food Administration (DVFA) as part of the agreement with Aarhus University on research-based policy support, as well as by Aarhus University. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The reviewer ND declared a past collaboration with one of the authors MH to the handling Editor.
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.
The authors thank the Danish pig farmer Niels Aage Arve and his staff for providing piglets and facilities for the study and for their flexibility. Technicians from Aarhus University involved in the project are acknowledged for their hard work and dedication. We also thank Karoline V. Dohrmann for her help in the data analysis, Hanne Kongsted, Aarhus University, for her qualified advice in the design of the study, and Torben Larsen, Aarhus University, for helping developing the saliva sampling method and conducting the cortisol assays.
The Supplementary Material for this article can be found online at:
Video of the intra-testicular injection procedure.
Dataset used for statistical analysis.
The adapted castration bench used during injection, castration and sham handling. Picture of the bench
Description of the parameters used for calibration of the band limited energy automatic detection of calls in the Raven Pro software.
Saliva cortisol concentrations recorded for each sampling time.