Abstract

In recent years, the Zoological Society of San Diego has made a significant effort to establish captive breeding populations of six species of exotic swine, including the babirusa (Babyrousa babyrussa celebensis), Bornean bearded pig (Sus barbatus barbatus), Chacoan peccary or tagua (Catagonus wagneri), European wild boar (Sus scrofa scrofa), red river hog (Potamochoerus porcus) and southern warthog (Phacochoerus africanus sundevallii). In addition, the petting zoo maintains two adult castrated Vietnamese pot-bellied pigs (Sus scrofa F. domestica). Routine husbandry and medical management of these species require consistently reliable chemical immobilization protocols.

In 1992, after encountering problems associated with less-than-desirable recovery from anesthesia using cyclohexylamines in red river hogs immobilized with tiletamine and zolazepam (Telazol), one of the authors (Morris) began surveying the literature for sedative/anesthetic alternatives to cyclohexylamines in swine species. The main goal of this search was to find a set of drugs that, when used as a combination, would produce complete and reversible immobility with manageable side effects. A literature search for information on anesthetic combinations in swine was conducted. Among the many citations retrieved, combinations of ketamine, xylazine and climazolam;² midazolam alone;⁶ and butorphanol, xylazine and ketamine⁴ were attractive prospects. Another paper reporting on the effects of butorphanol combined with medetomidine in swine⁵ was of particular interest.

Despite its attractiveness as a possible immobilization agent in exotic swine, medetomidine was not widely available, so combinations of butorphanol with xylazine and detomidine were evaluated in the two pot-bellied pigs at the petting zoo. Doses of 0.3 mg/kg butorphanol combined with 2 mg/kg xylazine, and butorphanol at the same dose combined with 100 µg/kg produced profound sedation but were easily aroused. However, when midazolam 0.3 mg/kg was added to these two combinations, complete immobility with relaxation and analgesia was observed in the pot-bellied pigs (P.J. Morris, unpublished data). Using this combination, one of the authors (Morris) castrated the two petting zoo pigs using nothing more than local lidocaine infiltration into the spermatic cord of the patients during surgical preparation. At the end of surgery, a combination of yohimbine (0.3 mg/kg) and naltrexone (50-mg total dose) was given, which resulted in rapid and smooth reversal of immobility. Subsequently, several combinations of xylazine, midazolam and butorphanol or detomidine, midazolam and butorphanol were used in babirusa, European wild boar, red river hogs, warthogs, and to evaluate the efficacy of these protocols in other exotic swine species. Though significant effects were observed in warthogs and European wild boar using detomidine at 100–125 mg/kg with butorphanol at 300 µg/kg and midazolam at 300 mg/kg, these two species were consistently easy to arouse during sedation, forcing the use of adjuncts such as low doses of Telazol and ketamine. However, in red river hogs, the use of this combination consistently resulted in complete immobility with smooth, rapid, and complete recovery upon injection of yohimbine at 300 µg/kg and naltrexone at 25–50 mg total dose as a mixture given intravenously.³

With the increased availability of medetomidine in recent years, the authors began testing the combination of medetomidine, butorphanol and midazolam in these seven swine species with significantly improved results compared to similar combinations including xylazine or detomidine. At this point, the combination of midazolam, butorphanol and medetomidine (MBM) has provided consistent and optimal results in all the suid species within our collection, and it is now the preferred anesthetic option for general chemical immobilization and/or for induction of inhalant anesthesia of all swine at the San Diego Zoo.

Though the results of MBM sedation in swine species studied are highly desirable and consistently reproducible, the volume of injection with this combination is excessive. Frequently two darts must be employed to deliver the entire dose to larger animals. In addition, this combination is more expensive to use than other alternatives, such as combinations of Telazol and xylazine.¹ Still, one of the most expensive drugs employed routinely in the antagonism of the zolazepam fraction of Telazol (flumazenil) is one of the most expensive drugs in these protocols. As a result, the apparent cost savings associated with the use of Telazol are significantly hampered when flumazenil is used routinely as an antagonist in any protocol.

Sedation in swine immobilized with MBM results in fair to good analgesic effects and excellent relaxation, including significant jaw tone relaxation—a quality not observed in our situation using other protocols. Hypoxemia, hypotension, bradypnea and bradycardia are the predictable side effects resulting from the use of MBM in swine (as well as in other species at the San Diego Zoo not reported here). Changes in cardiopulmonary physiology have been reported in swine associated with the use of medetomidine and butorphanol,^4,5 as well as with the use of midazolam.⁶ Minimum patient monitoring recommendations to be used in association with MBM in swine include pulse oximetry with intermittent temperature, pulse and respiration observations. In addition, supplemental oxygen via nasopharyngeal insufflation with a soft rubber cannula at 4–6 L/minute effectively combats hypoxemia as measured by observing trends in pulse oximetry. At the time of preparation of this abstract, only one mortality has been associated with the use of this protocol. In this case the patient, an aged babirusa, was observed to have cardiac disease on postmortem examination. This combination has been used repeatedly and successfully in animals less than 1 year to over 10 years of age in the swine species listed.

Antagonism of MBM sedation has been achieved mainly through IM injection of a mixture of naltrexone at approximately 350–700 mg/kg and atipamezole at 100–350 µg/kg as a single IM injection. Time from injection to standing posture varies, but in most cases, animals are standing within 10 minutes post antagonist injection (PAI). In all cases, signs of antagonist effects start with increased respiratory rate and depth. In most cases, animals will rapidly regain sternal and/or standing posture within 3–7 minutes after this initial increase in respiratory rate. However, in some cases, animals remain recumbent despite noticeable increases in respiratory rate and depth. In these cases, flumazenil at 1:10–1:20 flumazenil:midazolam has resulted in complete recovery within 5 minutes of flumazenil injection IM in all cases studied to date. The use of flumazenil in every case is warranted for optimal antagonism of effects, but as mentioned previously, the cost of this drug may be prohibitive. As a result, we use flumazenil only in refractory cases where naltrexone and atipamezole fail to yield the desired antagonist effects. Finally, through sequential reductions in the dose of atipamezole, we now recommend dose ranges of 80–100 mg/kg routinely for reversal of medetomidine effects in swine species. In most cases, swine will remain quiet with variable appetite for 24 hours after the use of this combination. In one group of four warthogs immobilized with MBM, all four individuals were unusually quiet and inappetent for 48 hours after antagonism. Flumazenil had to be employed to completely antagonize MBM in these individuals. This suggests a lingering effect of midazolam may have played a role in the effects observed in these cases. However, by 72 hours PAI all four animals were normal, and no further problems were observed in this group.

In conclusion, through the clinical evaluation of several combinations (Table 1), MBM has emerged as the preferred combination for chemical immobilization and general anesthetic induction in Suidae at the San Diego Zoo.

Table 1. Recommendations for various drug combinations for chemical immobilization of swine. All six protocols have been used with favorable results in clinical cases at the San Diego Zoo. Doses for narcotic antagonists are empirical and based on clinical response only. It is recommended that all antagonists be given intramuscularly only to prevent hyperexcitability during recovery. Darkened spaces represent untested combinations for which no recommendations are offered. In all cases, if flumazenil is required, we recommend a dose range of 1:10–1:20 flumazenil:midazolam and only to reverse effects of midazolam when incorporated into the protocol. In cases where a protocol may have more than one recommendation for an antagonist pair, only use ONE PAIR to antagonize the sedative effects for that protocol.

Det=Detomidine, Med=Medetomidine, Xyl=Xylazine, Mid=Midazolam, Tel=Telazol, But=Butorphanol, Ati=Atipamezole, Yoh=Yohimbine, Nal=Naltrexone, Nar=Narcan
All doses are in micrograms per kilogram (µg/kg).
*The preferred protocol is in bold (protocol #3).

Acknowledgments

The authors would like to thank the staff of the Veterinary Services Department of the San Diego Zoo as well as the Mammal Department for years of hard work that have contributed to the development of these protocols. In addition, the authors would like to thank the many veterinarians who have used these combinations over the years, for sharing their observations of the use of these combinations in suid species.

Literature Cited

1.  Calle, P.P. and P.J. Morris. Anesthesia for nondomestic suids. In: Fowler, M.E. and R.E. Miller (eds). Zoo and Wild Animal Medicine: Current Therapy IV. W.B. Saunders Company, 1999. Pp. 639–646.

2.  Ganter M. and M. Kanngiesser. 1991. Effect of ketamine and its combinations with xylazine and climazolam on the circulation and respiration in swine. Zentralbl Veterinarmed [A] 38(7):501–509.

3.  Morris, P.J. 1996. Recent developments in anesthesia of exotic ungulates. The North American Veterinary Conference Veterinary Proceedings (10):901–902.

4.  Nishimura R., M. Sakaguchi, M. Mochizuki, N. Sasaki, H. Takahashi, H. Tamura, and A. Takeuchi. 1992. A balanced anesthesia with a combination of xylazine, ketamine and butorphanol and its antagonism by yohimbine in pigs. J Vet Med Sci 54(4):615–620.

5.  Sakaguchi M., R. Nishimura, N. Sasaki, T. Ishiguro, H. Tamura, A. Takeuchi. 1992. Enhancing effect of butorphanol on medetomidine-induced sedation in pigs. J Vet Med Sci 54(6):1183–1185.

6.  Smith A.C., J.L. Zellner, F.G. Spinale, M.M. Swindle. 1991. Sedative and cardiovascular effects of midazolam in swine. Lab Anim Sci 41(2):157–161.