Abstract

Takin (Budorcas taxicolor) are large, stocky members of the bovid subfamily caprinae from Western China and the Himalayas. Typical habitat for takin is described as upper elevation zones from 6,500-15,000 feet above sea level. Takin typically live in groups, often numbering several hundred in summer foraging grounds. During the winter these larger groups split up and descend to lower elevations to forage. While grazing is the main daily activity for this species, they are typically crepuscular grazers. When not grazing, takin can be found hiding in cover vegetation. Females typically give birth to single young every other year in the wild. Young takin are observed to nurse for up to 9 mo before being completely weaned.¹

In the mid to late 1980s the Zoological Society of San Diego began acquiring Sichuan and Mishmi takin to begin breeding programs for these two subspecies in North American Zoos. In captivity, the main clinical problem encountered in our institution have been dystocias and/or retained placentas associated with metritis and founder. Hoof overgrowth is another typical problem of this species in captivity. Older takin tend to develop a ringbone-like arthritis requiring long-term palliative therapy with polysulfated glycosaminoglycans and nonsteroidal anti-inflammatory agents. Initially, etorphine (M-99; Leommon Co., Sellersville, PA) and xylazine (Rompun; Bayer Agriculture, Animal Health Division, Shawnee, KS) were used to sedate takin for routine medical/management procedures. As carfentanil (Wildnil; Wildlife Pharmaceuticals, Fort Collins, CO) became more available, etorphine was replaced with carfentanil. While effective, xylazine/carfentanil sedations typically were associated with apnea and ruminal regurgitation leading to an increased potential for aspiration.

Concern over the increased potential for aspiration pneumonia and complications resulting from apnea stimulated the search for an improved chemical restraint protocol for this species. Early in 1997 the veterinary staff at the San Diego Zoo began using a combination of (Domitor; Pfizer Animal Health, Exton, PA) and butorphanol (Torbugesic; Fort Dodge Animal Health, Fort Dodge, IA) for routine procedures in young animals being prepared for shipment to other institutions. Surprisingly, this combination consistently yielded profound sedative effects with little or no ruminal regurgitation. Soon, the combination was being used in larger females with reproductive problems, and finally in the largest males. Currently, the combination of medetomidine and butorphanol is the preferred protocol for routine sedation of the two subspecies at the San Diego Zoo. Table 1 summarizes the chemical immobilization data collected from immobilization records for Sichuan and Mishmi takin at the San Diego Zoo. A total of 83 records (67 on Sichuan and 16 on Mishmi takin) were evaluated for inclusion in a review of takin chemical immobilization protocols at the San Diego Zoo. Records were selected based on the following criteria:

1.  Complete recorded data. In some cases essential data about the event were not recorded--these cases were discarded.

2.  Uncomplicated cases. Case selection included simple procedures with nearly identical repetitious steps such as routine hoof maintenance, simple rechecks of medical cases or pre-shipment examinations.

3.  Cases lasting less than or equal to 1 hr duration.

4.  Cases where intravenous ketamine (Ketaject; Phoenix Pharmaceuticals, St. Joseph, MO) was the only adjunct used to maintain sedation after the initial induction dart.

5.  Cases where an accurate body weight was measured on the day of the immobilization.

Of the records fitting these criteria, 25 cases (4 males, 21 females) sedated with a xylazine/carfentanil (X/C) combination were selected to compare with 25 cases (13 males, 12 females) sedated with a medetomidine/butorphanol (M/B) combination. In all 6 Mishmi takin and 44 Sichuan takin anesthetic events were included, representing immobilization events from a total of 17 individuals (6 Mishmi takin and 11 Sichuan takin). Immobilization data (mean, sem) for all takin sedated with XC as well as all male, all female, and total takin sedated with MB are summarized in Table 1. Female takin immobilized with carfentanil and xylazine are over represented in the data set, due to the fact that reproductive problems requiring examinations dominated the medical efforts of the group early on. As time passed, the herd began to breed successfully, and more immobilizations were required for preship examinations and hooftrims, in addition to reproductive examinations. Age and body weight data were similar for both XC and MB groups.

Subjectively, comparing the sedative effects of these two protocols, immobilization with medetomidine and butorphanol produces a smoother induction with more stable vital signs, results in rare regurgitation episodes, and consistently smooth recoveries after antagonism. Based on immobilization data, takin sedated with XC had initial onset and recumbency times that averaged 2 min faster than when MB was used. Inductions tended to be smooth, with animals often standing calmly after darting until slowly dropping into sternal or lateral recumbency. Typically, XC sedated takin would fall into lateral recumbency while MB sedated takin tended to remain in sternal recumbency until physically repositioned into lateral recumbency.

During sedation, mean percent oxygen saturation of hemoglobin (SpO₂) measurements were recorded using the tongue as the preferred site for sensor placement. Measurements were made at the beginning of sedation and monitored for significant changes during sedation. Values represented here are initial oximetry values before and after nasal supplementation with 100% oxygen. Side effects of XC sedated takin included apnea and low SpO₂ values, and increased tendency to regurgitate ruminal contents. Side effects of MB sedated takin included bradycardia and low Sp₂O values. In both XC and MB sedated groups, mean SpO₂ values were lower and more variable before intranasal oxygen supplementation. After nasal oxygen supplementation, mean SpO₂ values were above 90% with minimal variability between sedation events. In both groups takin tended to be relaxed, but relaxation was superior in MB sedated takin. In some cases animals struggled under sedation such that an adjunct sedative was required. In the cases represented here, supplemental ketamine boluses were required in 5 of 25 XC sedated takin, while ketamine bolus supplements were required in only 2 of 25 MB sedated takin. No regurgitation episodes were reported for the takin in the MB sedated group, while 6 of 25 XC sedated takin regurgitated rumen contents during sedation. There were no deaths and no unusual morbidity in the cases comparing pre and post sedation health records.

There was no significant difference in total sedation time from initial darting to administration of reversal agents between XC and MB groups. Antagonism of xylazine was accomplished with yohimbine (Antagonil; Wildlife Pharmaceuticals, Fort Collins, CO), medetomidine with Atipamezole (Antisedan; Pfizer Animal Health, Exton, PA USA), and carfentanil with naltrexone (DuPont Merck, Wilmington, DE). After administration of antagonists, takin sedated with XC recovered an average of 2 min faster than the MB sedated group.

In summary, both Sichuan and Mishmi takin respond excellently to a combination of butorphanol at 0.2-0.25 mg/kg with medetomidine at 0.03 mg/kg. Inductions tend to be smooth, and immobility is typically complete with good relaxation. Notable side effects include bradycardia and low SpO₂ values. Nasal insufflation with 100% oxygen at 4-6 L/min helps to maintain good oxygen saturation values through the duration of sedation. Reversal with 0.35 mg/kg naltrexone and 5:1 atipamezole:medetomidine given as a combination i.m. typically results in a smooth recovery 7-8 minutes after administration of antagonists. Injection volume is a problem with 1 mg/ml medetomidine, but this problem will be resolved once a concentrated product becomes available.

Table 1. Takin immobilization data summary.

Data represented as average and standard error of the mean. All doses in mg/kg. Abbreviations: wt = weight in kg, but = butorphanol dose, carf = carfentanil dose, med = medetomidine dose, xy = xylazine dose, ati = atipamezole dose, nal = naltrexone dose, yo = yohimbine dose, ie = time of initial effect after darting (min.), dn = time of sternal or lateral recumbency after darting (min.), tot = total procedure time before reversal (min.), rev = time after reversal until standing, Sp- = SpO₂ before nasal oxygen supplement, Sp+ = SpO₂ during nasal oxygen supplementation, T = rectal temperature, P = pulse (beats/min.), R = respiratory rate (breaths/min.). For medetomidine/butorphanol data mean A, sem A = mean and sem for all takin sedated with medetomidine/butorphanol; mean M, sem M = mean and sem of all male takin sedated with medetomidine/butorphanol, mean F, sem F = mean and sem of all female takin sedated with medetomidine/butorphanol.

References

1.  Nowak RM. (ed.). 1998. Walker's Mammals of the World. vol.II. The Johns Hopkins University Press.