Abstract

Introduction

Wild pigs have become more commonly exhibited in North American zoos. The suborder Suina contains two families, the Suidae and the Tayassuidae. There are 13 species in five genera belonging to the family Suidae with members found in Europe, Asia, East Indies and Africa. The family Tayassuidae is formed by three species in two genera found exclusively in the American continent. Different protocols for chemical immobilization in these two families have been described elsewhere.⁵ The use of midazolam, butorphanol, and medetomidine (MBM) for routine sedation of pigs and peccaries has provided overall good, consistent results in the greatest number of swine species at the San Diego Zoo and is one of the recommended protocols for routine chemical restraint suggested by the TAG veterinary advisor.^4,6,7 However, hypoglycemia has been reported with the use of this anesthetic protocol.^4,6,7 Other protocols reported for Suidae and Tayassuidae species have not reported this effect on glucose blood levels in sedated specimens, pigs or peccaries.⁵ Hypoglycemia is a problem that requires immediate attention during a sedation episode; one wild pig anesthetized with the MBM protocol died after recovery from significant hypoglycemia.⁷ Hypoglycemia is a response not expected with the use of α-2 adrenergic agonists, since they tend to inhibit the insulin release from pancreatic β cells, resulting in a reduced glucose uptake in tissue and decreased glycogen production and storage in liver (hyperglycemia). This study compares the blood glucose levels in different species of anesthetized wild pigs in captivity at the San Diego Zoo, identifies those species that are susceptible to hypoglycemia, and establishes the reliability of a field diagnostic method for blood glucose.

Materials and Methods

Anesthesia reports were reviewed from 2000 to 2005 for glucose levels. Only complete records were selected for this study (convenience sample). A complete record was selected when blood glucose was reported by two measurement techniques: in-house laboratory (hexokinase, “in-house”) with Ciba-Corning Express Plus (Diamond Diagnostics©, Holliston, MA, USA) and field testing with FreeStyle™ (“field”) glucometer (Abbott Laboratories, Abbott Park, IL, USA) in the same anesthetic event, and where the anesthetic protocol employed was MBM. A total of n=92 anesthetic events were selected for the study, including the following species: European wild boar (Sus scrofa, n=7), Visayan warty pig (Sus cebifrons, n=19), Bornean bearded pig (Sus barbatus, n=10), red river hog (Potamochoerus porcus, n=33), African bush pig (Potamochoerus larvatus, n=5), South African warthog (Phacochoerus africanus sundevallii, n=10) and Chacoan peccary (Catagonus wagneri, n=8). Reported normal blood glucose values in domestic swine are 85–150;⁸ for this study, blood glucose of <70 mg/dl was considered hypoglycemic. Descriptive central tendency and dispersion parameters of blood glucose levels were obtained for both measurement techniques. Kruskal-Wallis one-way ANOVA was used for determination of difference in blood glucose levels among species, and a Wilcoxon rank sum test was used to identify those differences (in-lab results). These same analyses were repeated for the blood glucose results using the FreeStyle™ glucometer. A paired t-test was performed between in-house laboratory results and FreeStyle™ blood glucose results in order to determine reliability of the field blood glucose method. Minitab® statistical software (Minitab Inc., State College, PA, USA) was used for the analyses.

Results

Table 1 shows the descriptive values for blood glucose in the different species of pigs. Kruskal-Wallis one-way ANOVA results were significantly (p≤0.05) different among the different species with both diagnostic methods. The Wilcoxon rank sum test identified red river hogs and African bush pigs as having blood glucose values significantly lower (p≤0.05) than the established minimum and different from other species of wild swine using the in-house laboratory diagnostic method, while red river hogs, African bush pigs, Visayan warty pigs and South African Warthogs were found to be significantly lower than the minimum using the field technique. The in-house and field techniques were statistically different in some wild swine species (see Table 1). It is important to note that the sample populations did not follow a normal distribution, requiring the use of nonparametric statistical analyses.

Table 1. Description and comparison of blood glucose values obtained by in-house and FreeStyle™ glucometer in seven different species of wild swine anesthetized with medetomidine-butorphanol and midazolam at the San Diego Zoo from 2000–2005

^ap≤0.05 significant difference between both blood glucose measurements

Discussion

Hypoglycemia was seen consistently using both blood glucose diagnostic methods in two species of African wild swine belonging to the same genus (Potamochoerus sp.): red river hogs and African bush pigs. Two other species were considered susceptible to hypoglycemia using the FreeStyle™ (field) glucometer: one from Africa (Phacochoerus africanus sundevallii) and one from Asia (Sus cebifrons). The findings found in the Potamochoerus sp. are consistent with clinical observations during several years of anesthetic procedures. The differences in the results using both diagnostic methods in Phacochoerus spp. and Sus cebifrons may be attributed to the small sample size and distribution curves. In these two species there was no detectable hypoglycemia using the in-house laboratory diagnostic, but hypoglycemia was detected with the FreeStyle™ glucometer. This could suggest that different calibration is required for the field technique in these species. Care should be taken when interpreting results in the field for these two species. Our results rejected the hypotheses that Visayan warty pigs will also be susceptible to hypoglycemia using both methods. However, based on our clinical observations, they should still be considered susceptible until further studies with larger sample sizes are conducted. Hyperglycemia has been seen in medetomidine-ketamine-treated animals, and similarly increasing the xylazine dose in tigers produced higher glucose levels. There is no physiologic explanation for why members of the genus Potamochoerus sp. suffer from hypoglycemia instead of hyperglycemia as in other species of animals.

Conclusion

Wild swine of the genus Potamochoerus sp. should be considered highly susceptible to develop hypoglycemia under anesthesia using the MBM anesthetic combination. The use of a field technique (FreeStyle™) for the assessment of blood glucose seems to be reliable in the genus Potamochoerus sp., but care should be taken when interpreting results in other wild swine species. Further studies are needed to understand how glucose metabolism is influenced by anesthetic drugs. In addition, other potential factors such as individual, behavioral, and environmental stressors prior to anesthesia may be affecting blood glucose during anesthesia. Current studies are being performed in red river hogs and Visayan wart pigs in order to better characterize this phenomenon. When these species are anesthetized, it is strongly recommended that blood glucose levels be monitored closely in the early stages of the procedure. If hypoglycemia (<70 mg/dl) is noted, administration of 0.5–0.75 g/kg of dextrose IV bolus (slowly) should correct the deficit. Recheck the blood glucose hourly or just prior to recovery. Following anesthetic recovery, a small meal high in glucose-rich food items (grapes, melons, other fruits) should be offered to prevent a secondary hypoglycemic episode.

Acknowledgments

Laura Keener and the staff from the clinical pathology laboratory; the veterinary and animal management staff at the San Diego Zoo for their help in developing anesthesia protocols for wild suina and for assistance in collecting data; Scott Larsen for reviewing statistical analyses used in this report; and Deborah Lancman, Kay Munduate, and Donna Vader for assistance with medical records reviews.

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