Castration of piglets under CO2-gas anaesthesia

Abstract

It has become common practice in pig fattening production systems to castrate young boar piglets without the use of anaesthesia. In this study, we examined whether or not CO 2 gas is capable of inducing an acceptable anaesthetic state during which castration can be performed. The first step was to identify the most promising CO 2 /O 2 mixture. Based on the results from this first experiment, a mixture of 70% CO 2 1 30% O 2 was chosen for further investigation as a potential anaesthetic during the castration of young piglets. Thereby, it was established whether the duration and depth of anaesthesia were acceptable for castration where the animal has to be insensible and unconscious. Physiological effects were assessed based on electroencephalogram (EEG) and electrocardiogram (ECG) measurements, blood gas values and behavioural responses. During the induction phase, the only typical behaviour the piglets exhibited when exposed to the 70/30 gas mixture was heavy breathing. All piglets (n 5 25) lost consciousness after approximately 30 s according to the EEG. Heart rate decreased slowly during the induction phase, a serious drop occurred when piglets lost their posture. Immediately after this drop, the heart rate neared zero or showed a very irregular pattern. Shortly after loss of posture, most animals showed a few convulsions. None of the animals showed any reaction to castration in behaviour and/or on the EEG and ECG. On average, the piglets recovered within 59 s, i.e. EEG returned to its pre-induction pattern and piglets were able to regain a standing position. After 120 s, heart rate returned to pre-induction levels. In order to explore the usage range of CO 2 concentration, 24 piglets were exposed to 60% CO 2 1 20% O 2 1 20% N 2 for up to 30 s after loss of consciousness (as registered on EEG), and castrated after removal from the chamber. Sixteen of the 24 animals showed a reaction to the castration on the EEG. To establish the maximum time piglets survive in 70% CO 2 1 30% O 2 , five piglets were placed in this mixture for 3 min. Two of them died. After that, four piglets were placed in this mixture for 2 min after unconsciousness, one died after 2 min. It was concluded from this study that it is possible to anaesthetise piglets with a mixture of 70% CO 2 1 30% O 2, but that there are limits to its safety in terms of CO 2 concentration and duration of exposure. Before implementation for practical use, further research is essential to assess the limits of gas concentration and exposure times.

The effect of local or general anesthesia on the physiology and behavior of tail docked pigs

“…Furthermore, Kohler et al (1998) concluded that CO 2 anesthesia caused pig's considerable stress due to the struggling, vocalizations and strenuous breathing that was observed during induction. It has been suggested that lower CO 2 concentrations in combination with O 2 may decrease the aversion to CO 2 during induction (Gerritzen et al, 2008). In this study, the cortisol response to induction with 70% CO 2 tended to be higher than the response to induction with 100% CO 2 .…”

“…CO 2 is not currently a commonly used general anesthetic for surgical procedures as it known to be aversive to pigs and cause a sense of breathlessness (Raj and Gregory, 1995;Gregory, 2005). However, the advantages of using CO 2 as a method of anesthesia on-farm include, the speed at which CO 2 can be administered, the rapid reversal of anesthesia, the fact that CO 2 is not a restricted drug that has to be administered by a veterinarian and lastly there are no issues with drug residues (Gerritzen et al, 2008). In the literature, varying concentrations of CO 2 have been used to induce anesthesia in pigs (Kohler et al, 1998;Gerritzen et al, 2008).…”

“…However, the advantages of using CO 2 as a method of anesthesia on-farm include, the speed at which CO 2 can be administered, the rapid reversal of anesthesia, the fact that CO 2 is not a restricted drug that has to be administered by a veterinarian and lastly there are no issues with drug residues (Gerritzen et al, 2008). In the literature, varying concentrations of CO 2 have been used to induce anesthesia in pigs (Kohler et al, 1998;Gerritzen et al, 2008). Therefore, before the start of this experiment, a pilot study was conducted to determine if pigs would find a mixture of 70% CO 2 with 30% O 2 less aversive than 100% CO 2 .…”

“…General anesthetic agents cause a state of unconsciousness and thereby a complete absence of pain sensation. The ability of local and general anesthetic agents to effectively mitigate pain caused by painful husbandry procedures, such as tail docking and castration in lambs and pigs has been evaluated in the literature (McGlone et al, 1993;Graham et al, 1997;Kent et al, 1998;Gerritzen et al, 2008). However, research describing the efficacy of local or general anesthesia to alleviate pain caused by tail docking in pigs is limited.…”

“…However, the prolonged recovery period from these anesthetic agents could increase the risk of pigs being crushed by the sow and reduce feeding opportunities. Recently, carbon dioxide gas (CO 2 ) has been used to induce general anesthesia for castration in pigs (Kohler et al, 1998, Gerritzen et al, 2008. Among the advantages of using CO 2 to induce anesthesia to alleviate the pain caused by tail docking are the speed at which CO 2 can be administered, the rapid reversal of the anesthetic effects of this gas, the fact that CO 2 is not a restricted drug that has to be administered by a veterinarian, and lastly there are no issues with drug residues (Gerritzen et al, 2008).…”