Free-ranging yellow armadillos (Euphractus sexcinctus) from the Brazilian Pantanal were captured for surgical implantation of intra-abdominal radio transmitters. During March 2014, 11 animals were chemically immobilized with a combination of intramuscular ketamine hydrochloride, xylazine hydrochloride, midazolam maleate, and atropine sulfate. The mean induction time and initial heart rate in males was higher than in females. The sex of armadillos did not affect the respiratory rate, which increased from the beginning to end of the monitoring time. The rectal temperatures of females remained almost unchanged, whereas the rectal temperatures of males suffered a slight drop through the procedure. The mean (±SD) total surgical time was 50±6.5 min, and the total anesthetic recovery time was 2.5±0.5 h. The armadillos were monitored for 24 h after surgery and released at their capture site. The anesthetic association was effective, promoting muscle relaxation and analgesia that allowed the performance of surgical procedures.
The unusual anatomy of armadillos has challenged field researchers trying to attach external tracking devices on them, which makes the study of their spatial ecology difficult (Hernandez et al. 2010). Previous studies attached VHF transmitters or a packet containing a VHF transmitter plus a global positioning system device to the tail of armadillos (Medri 2008; Maccarini et al. 2015). However, the devices remained attached to their body only for a short period (maximum 31 d; Medri 2008).
To overcome the limitations of traditional attachment methods, the use of intraperitoneal transmitters may make long-term monitoring possible. For the surgical implantation of transmitters, the animals must be anesthetized to permit laparotomy. However, there are few reports of anesthesia in armadillos, and most of these studies focus on the nine-banded armadillo (Dasypus novemcinctus; Fournier-Chambrillon et al. 2000; Miranda and Costa 2007). One study mentioned anesthesia for yellow armadillos (Euphractus sexcinctus), but focused on semen collection (Sousa et al. 2016).
Our study was conducted at the Nhumirim Ranch (18°59′S, 56°39′W), an experimental station of Embrapa (Empresa Brasileira de Pesquisa Agropecuária [The Brazilian Agricultural Research Corporation]) located in the central Pantanal of Brazil. During March 2014, active searches were performed with vehicles on the ranch perimeter, and 11 yellow armadillos (seven adult females, three adult males, and one young male) were manually captured and transported to the ranch laboratory.
The initial proposed doses for immobilization was 15–30 mg/kg of ketamine hydrochloride (Quetamina, Vetnil, São Paulo, Brazil), 0.5 mg/kg of xylazine hydrochloride (Rompun, Bayer, São Paulo, Brazil), 0.5 mg/kg of midazolam maleate (Dormire, Cristália, São Paulo, Brazil), and 0.02 mg/kg of atropine sulfate (Atropina Fagra, Farmagrícola, Mairiporã, Brazil) by intramuscular injection in the pelvic limbs.
The body temperature of the animals and the ambient temperature were measured before drug administration, after which, we evaluated anesthetic induction time, surgery procedure total time, and total anesthetic recovery time (when animals were fully recovered from anesthesia and could potentially be released). The heart rate (HR) in beats per minute (bpm) and respiratory rate (RR) in respirations per minute (rpm) were evaluated immediately after anesthetic induction (time 0) and then every 10 min until the end of the surgical procedure. To allow statistical comparison between animals, we used measurements out to 40 min, which was the shortest duration of surgery. The HR was measured by cardiac auscultation and RR by direct observation. The rectal temperature (RT) was measured during the entire procedure with a digital thermometer with a precision of 0.1 C (J Prolab, São José dos Pinhais, Brazil).
The quality of the anesthetic protocol was evaluated by the response of anesthetized animals to surgical stimuli and by the degree of muscular relaxation, classified as good (no reaction to noxious stimuli caused by surgery and sufficient muscular relaxation), moderate (spontaneous movements in reaction to noxious stimuli or lack of muscular relaxation), or bad (spontaneous movements in reaction to noxious stimuli and lack of muscular relaxation).
After surgery, the animals received 75,000 UI/kg of a combination of benzylpenicillin, dihydrostreptomycin, and streptomycin (Pentabiótico Veterinário, Fort Dodge, Campinas, Brazil) and 0.1 mg/kg of meloxicam (Maxicam, Ouro Fino, São Paulo, Brazil), both by intramuscular injection.
We used an analysis of covariance to evaluate the relationship between induction time with the sex of the animals and their body weight. Repeated-measures analysis of variance was used to evaluate the relationship between the sex of the animals and their HR, RR, or RT at the start and end of monitoring. All analyses were conducted with R statistical software (R Development Core Team 2017).
The first armadillo, a female, received a combination of 15 mg/kg of ketamine hydrochloride, 0.5 mg/kg of xylazine hydrochloride, 0.5 mg/kg of midazolam maleate, and 0.02 mg/kg of atropine sulfate. This dosage was enough to provide only chemical restraint and superficial anesthesia. The induction time was 6.4 min, and the animal remained sensitive to the surgical procedure stimuli, showing spontaneous movements in reaction to noxious stimuli and requiring the administration of a second anesthetic dose (15 mg/kg of ketamine hydrochloride) to perform the skin incision. Hence, the data of this individual was not incorporated to the statistical analysis, and we doubled the ketamine dosage for subsequent armadillos, maintaining the dosage of the other drugs. After the first individual, the combination of 30 mg/kg of ketamine hydrochloride plus the other drugs at their original dosages was administered to 10 animals, resulting in good sedation, good muscle relaxation, and a proper surgical plan for transmitter implantation into the abdominal cavity.
Captured males tended to be lighter than females. However, there was no statistical interaction between body mass and sex to explain differences in induction time between males and females (t=1.757, df=6, P=0.13). According to the analysis of covariance (F2,7=4.815, P=0.05, R2=0.58), induction time was not related to body mass (−1.974, df=7, P=0.09), but males presented shorter induction time (1.7±0.5 min; t=−3.066, df=7, P=0.02) than females (3.2±1.4 min).
Sex and time interacted to explain the HR variation (F1,8=8.1, P=0.02), and visual examination of the graph (Fig. 1a) suggested that the initial mean HR (160±16 bpm) of males were higher than the initial mean HR (121±12 bpm) of females, although the HR of males and females did not differ at the end of the procedure (122±14 and 128±23, respectively). The RR was not related to sex (F1,8=0.548, P=0.48) and increased (F1,8=10.321, P<0.01) from 16.9 to 25.7 rpm from the beginning to the end of the monitoring time (Fig. 1b).
The RT varied with sex and monitoring time (F1,8=13.63, P<0.01); whereas the RT of females remained almost unchanged throughout the procedure (mean=34.5±0.9 to 34.3±0.8 C), the RT of males dropped slightly from 34.9±1.1 C immediately after anesthetic induction to 34.4±1.1 C after 40 min of anesthesia (Fig. 1c). During the study period, the mean ambient temperature was 29 C. However, room temperature during procedures varied between 30 and 35 C, with a mean of 33±0.8 C.
The mean surgery time for each armadillo was 50 min (range, 39–64 min). The animals were fit for release an average 2.5±0.5 h after anesthetic induction (time 0). No relationship between recovery time and sex (P=0.599) or body weight (P=0.672) was detected. The quality of the anesthetic protocol applied to 10 animals was considered good.
The dosages of ketamine hydrochloride used in this study were higher than those used for restraint and collection of biological samples from the Andean hairy armadillo (Chaetophractus nationi) by Rojas et al. (2013) and those used for semen collection from yellow armadillos (Sousa et al. 2016). In contrast, our ketamine dosage was smaller than that used for performing abdominal implantation in nine-banded armadillos (Hernandez et al. 2010). This is directly related to the synergy between the doses of different combinations of drugs used in anesthetic protocols and the intensity of stimuli caused by the type of procedure performed. The use of atropine is recommended to prevent sialorrhea during anesthesia in Xenarthra (Miranda and Costa 2007), a recommendation that we endorse, as anesthetized individuals in our study did not show excessive salivation.
In our study, anesthetic induction time in males was shorter than in females. However, induction time did not differ between sexes for other armadillo species, such as nine-banded armadillos, greater long-nosed armadillos (Dasypus kappleri), or three-banded armadillos (Tolypeutes matacus; Fournier-Chambrillon et al. 2000; Orozco 2011). The differences between sexes found in the present study could be related to the physical conditions of the animals, since females appeared to possess more subcutaneous adipose tissue than males.
The HR recorded during the procedure range between 100 and 180 bpm, values that were close to those reported by West et al. (2007) for armadillos (120–220 bpm). The high mean HR recorded at the beginning of the procedure may have been the result of the release of catecholamines before the anesthetic effect of xylazine or even as a response to the use of ketamine hydrochloride (Massone 2008); similar results were observed anesthetizing adult male Andean hairy armadillos (Rojas et al. 2013) and three-banded armadillos (Orozco 2011). The initial HR of males was higher than that of females. Our hypothesis is that body size may have influenced the HR, since males are smaller and consequently had a higher basal metabolic rate that is determined by an exponential relation with body size (Scholander et al. 1950).
Similar to results described by Fournier-Chambrillon et al. (2000), RR was variable between individuals, ranging between 3 and 56 rpm. The mean values in our yellow armadillos were below those previously reported: 60–80 rpm (West et al. 2007), 30 rpm in Andean hairy armadillo (Rojas et al. 2013), and 60 rpm in three-banded armadillo (Orozco 2011). However, bradypnea may not be very relevant to armadillos because of their fossorial habits, making them tolerant to long periods of apnea and hypoxemia (Hoff et al. 1982). The RR increased from the beginning to end of the monitoring time (40 min after anesthetic induction), which may be associated with painful stimuli caused by surgery. The incision was sutured between 30 and 40 min of the start of surgery in most animals, which coincided with the increased RR.
Xenarthrans are characterized by low body temperatures and low basal rates of metabolism when compared with other mammals of similar body mass. Furthermore, armadillos are imperfect homeotherms, which means that they have limited thermoregulatory capability (McNab 1985; Maccarini et al. 2015). In our study, the RT of females remained almost unchanged throughout the procedure, whereas the RT of males suffered a slight drop. The difference in RT between sexes may be related to adipose tissue thermogenesis.
Although animals were fully recovered from anesthesia in 2.5±0.5 h, we released them 24 h after the procedure. Because of their burrowing behavior, we wanted to avoid den utilization right after surgery, which could potentially increase the risk of infection and hinder healing. The anesthetic combination used in this study was effective, allowing the transmitter abdominal implantation procedure in yellow armadillos.
This study was carried out under the permission of Brazilian Ministério do Meio Ambiente through the Instituto Chico Mendes para Conservação da Biodiversidade (license 39873-3) and the Ethics Committee of the Universidade Federal de Mato Grosso do Sul (process 570/2013). We thank The Rufford Foundation, Embrapa Pantanal (Project SEG 02.10.06.007.00.02), Centro de Pesquisa do Pantanal/Ministério da Ciência e Tecnologia (grant 2008/CPP/13), and Fundação de Apoio ao Desenvolvimento do Ensino, Ciência e Tecnologia do Estado de Mato Grosso do Sul (FUNDECT; grant PRONEX-006/2015) for financial support. We thank Idea Wild and Neotropical Grassland Conservancy for equipment donation. We are grateful to FUNDECT for the scholarship awarded to N. Attias and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior for the scholarship awarded to G. Soresini.