S-ketamine and intranasal application: alternatives for the castration of male suckling piglets?

Ketamine, an Old-New Drug: Uses and Abuses

Ketamine as an old-new drug has a variety of clinical implications. In the last 30 years, ketamine has become popular for acute use in humans. Ketamine in standard doses is principally utilized for the induction and maintenance of surgical procedures. Besides its use in anesthesia and analgesia, recent studies have shown that ketamine has found a place in the treatment of asthma, epilepsy, depression, bipolar affective disorders, alcohol and heroin addiction. Ketamine primarily functions as a noncompetitive antagonist targeting the N-methyl-D-aspartate (NMDA) receptor, but its mechanism of action is complex. It is generally regarded as safe, with low doses and short-term use typically not leading to significant adverse effects. Also, ketamine is known as a powerful psychostimulant. During the past decade, ketamine has been one of the commonly abused drugs.

Efficacy of the intranasal application of azaperone for sedation in weaned piglets

The aim of the study was to compare the efficacy of the intranasal and parenteral administration of azaperone in order to achieve pig sedation. A total of 32 weaned piglets divided into 4 groups (8 piglets in each group) were used. Group A was injected intramuscularly (i.m.) with azaperone (Stresnil®, 40 mg/ml inj.; Elanco Animal Health) at a dose of 2 mg/kg of body weight (b.w.). Group B received a dose of 2 mg/kg b.w. of azaperone intranasally. Group C was given azaperone intranasally at a dose of 4 mg/kg b.w. Group D was given 1 ml of saline intranasally and served as the control group. The response to the defined stimulus (a blunt blow of a metal rod into a metal edge of a pen), the degree of salivation, movement level, body temperature and serum azaperone concentration were included in the trial. We found that in order to induce an adequate level of sedation comparable to the standard method of application, i.e., 2 mg/kg b.w. i.m., the intranasal administration of azaperone at a dose of 4 mg/kg body weight is required.

How is depth of anaesthesia assessed in experimental pigs? A scoping review

BACKGROUND

Despite the large number of pigs involved in translational studies, no gold standard depth of anaesthesia indicators are available. We undertook a scoping review to investigate and summarize the evidence that sustains or contradicts the use of depth of anaesthesia indicators in this species.

METHODS

Medline, Embase and CAB abstract were searched up to September 22nd 2022. No limits were set for time, language and study type. Only original articles of in vivo studies using pigs or minipigs undergoing general anaesthesia were included. The depth of anaesthesia indicators reported in the selected papers were divided in two categories: A, indicators purposely investigated as method to assess depth of anaesthesia; B, indicators reported but not investigated as method to assess depth of anaesthesia.

RESULTS

Out of 13792 papers found, 105 were included after the screening process. Category A: 17 depth of anaesthesia indicators were found in 19 papers. Studies were conducted using inhalant anaesthetics as the main anaesthetic agent in the majority of the cases (13/19 = 68.4%), while 3/19 (15.8%) used propofol. The most investigated depth of anaesthesia indicators were bispectral index (8/19 = 42.1%) and spectral edge frequency 95% (5/19 = 26.3%). Contrasting results about the specific usefulness of each depth of anaesthesia indicators were reported. Category B: 23 depth of anaesthesia indicators were found in 92 papers. The most reported depth of anaesthesia indicators were: motor response following a stimulus (37/92 = 40.2%), depth of anaesthesia scores (21/92 = 23.3%), bispectral index (16/92 = 17.8%) and spectral edge frequency 95% (9/92 = 9.8%).

CONCLUSION

Results highlight the lack of scientifically valid and reliable indicators to ensure adequate depth of anaesthesia in pigs.

[Comparison of the efficiency of inhalation and injection anaesthesia for the castration of male suckling piglets in different organic farms]

OBJECTIVE

In Germany, injection and inhalation anesthesia with the addition of an analgesic drug are an interim solution to surgical castration under general anesthesia due to the ban on non-anesthetic castration of male suckling piglets under 8 days of age. However, the efficiency of both anesthetic procedures is submit to controversial discussion. Most of the studies addressing this question only examined one of the procedures in comparison to piglets castrated without anesthesia or uncastrated controls. Comparisons between the anesthesia methods, especially under conditions of organically working farms, are almost completely lacking. The aim of the present study was therefore to compare the efficacy of injection and inhalation anesthesia under practical conditions in 7 organic farms as well as to examine the effect of metamizole administered in addition to meloxicam.

MATERIAL AND METHODS

For this purpose, 514 male suckling piglets were examined with regard to anesthesia efficiency (reflex test, defence behaviour), body temperature, post-operative bleeding and wound healing, post-operative behavior and pain behavior as well as the course of the recovery phase.

RESULTS

The results show a basic superiority of inhalation anesthesia over injection anesthesia, especially in the areas of anesthetic efficacy, thermoregulation and duration of the recovery phase. In 7.7 to 15 % of piglets, the perianal and interclaw reflexes studied were still present at the time of castration. Following injection and inhalation anesthesia, in total 83.6 (25.2 %) of the piglets showed at least one of the following criteria: positive reflex response, clear defensive movements or vocalisations. Body temperature dropped by 0.41 °C under inhalation anesthesia and by 1.82 °C under injection anesthesia. Post-castration bleeding and wound healing were hardly influenced by the type of anesthesia. Almost all piglets showed signs of pain and pain-associated behavior for 5 and 72 hours after castration, regardless of the type of anesthesia. The post-castration recovery phases lasted significantly longer after injection anesthesia (107 minutes) than following inhalation anesthesia (33.3 minutes) until the piglets were returned to the sow.

CONCLUSION

Neither injection nor inhalation anesthesia in spite of additional administration of meloxicam, nor the supplementary use of metamizole, fulfil the EU requirements for painless castration.

CLINICAL RELEVANCE

The necessary analgesia during and after castration of male suckling piglets is not achieved under either isoflurane or ketamine/azaperone anesthesia, despite the use of meloxicam and metamizole.

Welfare of pigs on farm

This scientific opinion focuses on the welfare of pigs on farm, and is based on literature and expert opinion. All pig categories were assessed: gilts and dry sows, farrowing and lactating sows, suckling piglets, weaners, rearing pigs and boars. The most relevant husbandry systems used in Europe are described. For each system, highly relevant welfare consequences were identified, as well as related animal-based measures (ABMs), and hazards leading to the welfare consequences. Moreover, measures to prevent or correct the hazards and/or mitigate the welfare consequences are recommended. Recommendations are also provided on quantitative or qualitative criteria to answer specific questions on the welfare of pigs related to tail biting and related to the European Citizen's Initiative 'End the Cage Age'. For example, the AHAW Panel recommends how to mitigate group stress when dry sows and gilts are grouped immediately after weaning or in early pregnancy. Results of a comparative qualitative assessment suggested that long-stemmed or long-cut straw, hay or haylage is the most suitable material for nest-building. A period of time will be needed for staff and animals to adapt to housing lactating sows and their piglets in farrowing pens (as opposed to crates) before achieving stable welfare outcomes. The panel recommends a minimum available space to the lactating sow to ensure piglet welfare (measured by live-born piglet mortality). Among the main risk factors for tail biting are space allowance, types of flooring, air quality, health status and diet composition, while weaning age was not associated directly with tail biting in later life. The relationship between the availability of space and growth rate, lying behaviour and tail biting in rearing pigs is quantified and presented. Finally, the panel suggests a set of ABMs to use at slaughter for monitoring on-farm welfare of cull sows and rearing pigs.