Xylazine and a xylazine/fentanyl citrate/azaperone combination in farmed deer. II: velvet antler removal and reversal combinations

Three studies were undertaken on farmed red and red x wapiti deer to evaluate xylazine and a xylazine/fentanyl citrate/azaperone combination for velvet antler removal. In the first experiment, 30 1-2 year-old red and 25% red x wapiti deer whose velvet was to be removed were given either 5% xylazine alone at 0.5 mg/kg body weight intramuscularly or the same dose rate of a commercially available mixture of 5% xylazine with the addition of 0.4 mg of fentanyl citrate and 3.2 mg of azaperone per ml. Physiological, behavioural and analgesic responses and reversal times after yohimbine or yohimbine and naloxone were monitored. There were no differences in heart rate, respiration rate, sedative or analgesic properties detected between xylazine or the xylazine/fentanyl citrate/azaperone combination. All deer became recumbent, but those given the xylazine/fentanyl citrate/azaperone combination became recumbent more rapidly than those given xylazine alone (9.4 and 12.5 minutes, respectively, p<0.05). The arousal pattern and timing of reversal of xylazine and xylazine/fentanyl citrate/azaperone using yohimbine and yohimbine and naloxone, respectively, were similar. The second experiment evaluated the reversal of the xylazine/fentanyl citrate/azaperone combination with either yohimbine or yohimbine and naloxone in 43 3-year-old red deer stags after velvet antler removal. There were no differences in arousal pattern or time to standing between reversal treatments. Sixteen 1-year-old red and 25% red x wapiti stags were used in the third experiment to evaluate clinically the analgesic properties of xylazine and xylazine/fentanyl citrate/azaperone combination during velvet removal without the application of a local anaesthetic agent. Withdrawal responses were observed in most deer after the xylazine/fentanyl citrate/azaperone combination at dosages containing 0.5, 0.7 and 0.75 mg of xylazine/kg and after xylazine alone at 0.7 mg/kg, indicating that insufficient analgesia was provided by the systemic agent for the surgical procedure of velvet antler removal. These studies have shown that the knock-down effect of the xylazine/fentanyl citrate/azaperone combination was more rapid than that of xylazine alone, but that other physiological, behavioural and analgesic responses at doses used and evaluated by the methods used were similar. Reversal of both the xylazine and xylazine/fentanyl citrate/azaperone combination was similar when using either yohimbine alone for xylazine and the xylazine/fentanyl citrate/azaperone combination or yohimbine and naloxone for the xylazine/fentanyl citrate/azaperone combination. The evaluation of surgical analgesia for antler removal suggested that both xylazine alone and the xylazine/fentanyl citrate/azaperone combination provided insufficient analgesia and that local anaesthetic should be used in all cases.     

Pharmacokinetics and pharmacodynamics of carfentanil and naltrexone in female common eland (Taurotragus oryx).

The pharmacokinetic parameters of carfentanil and naltrexone were determined in the common eland (Taurotragus oryx). Six adult females were immobilized with xylazine (0.23 +/- 0.03 mg/kg i.m.) and carfentanil (0.0169 +/- 0.0005 mg/kg i.m.) for a 45-min period, during which time routine health care procedures were performed. Heart and respiration rates and body temperatures were monitored throughout the immobilization period. A single intramuscular injection of naltrexone (1.66 +/- 0.08 mg/kg i.m.) was sufficient for reversal. The eland were intermittently restrained in a hydraulic squeeze chute for serial blood sample collection via jugular venipuncture during immobilization and up to 48 hr post-immobilization. The quantification of carfentanil and naltrexone in the plasma was performed by liquid chromatography and mass spectroscopy methods. Carfentanil was rapidly absorbed following administration, with the peak plasma concentration (C(max)) at 13.8 min. Naltrexone was readily absorbed and reached C(max) at 23.4 +/- 16.8 min after administration. All animals stood 2.7 +/- 2.2 min after naltrexone administration. Carfentanil has a half-life of 7.7 hr, whereas naltrexone has a much shorter half-life of 3.7 hr. Although respiratory rates appeared to fluctuate widely among animals, heart rates and body temperature remained stable throughout the immobilization. Renarcotization was not noted as a major complication.     

Pharmacology of narcotic analgesics in the horse: selective blockade of narcotic-induced locomotor activity

The locomotor responses of horses given morphine and fentanyl were blocked or lessened by administration of naloxone or acepromazine. Naloxone given at the dosage of 0.015 mg/kg completely blocked the locomotor activity induced in horses given fentanyl (0.020 mg/kg of body weight). The locomotor stimulation produced by morphine given at the dosage of 2.4 mg/kg was reduced by 75% of naloxone (0.020 mg/kg). Acepromazine partially blocked the locomotor responses to fentanyl and morphine. This blockade activity reached its peak about 30 minutes after acepromazine was given (IV) and lasted more than 6 hours. Simultaneous administration of acepromazine and morphine was associated with substantial respiratory depression for more than 4 hours after administration of both drugs. In other experiments, fentanyl did not add to the partial locomotor response observed after large doses of pentazocine were given--this being consistent with the concept that pentazocine possesses both antagonist and agonist actions at the narcotic receptor. Furosemide and phenylbutazone, given at usually used clinical doses, had no effect on the locomotor response to fentanyl, indicating that the usual clinical dosages of neither drug exerted stimulant or depressant actions.     

Reversible anesthesia of captive California sea lions (Zalophus californianus) with medetomidine, midazolam, butorphanol, and isoflurane.

Two adult California sea lions (Zalophus californianus) were effectively anesthetized 13 times with medetomidine (0.010-0.013 mg/kg), midazolam (0.2-0.26 mg/kg), and butorphanol (0.2-0.4 mg/kg) by i.m. hand or pole syringe injection. For each anesthetic event, atropine (0.02 mg/kg, i.m.) was administered 6-20 min after initial injections, and oxygen administration via face mask or nasal insufflation began at the same time. Light anesthesia was induced in 8-22 min and lasted 13-78 min. During eight of the procedures, isoflurane (0.5-2.0%) was administered via face mask or endotracheal tube for an additional 30-120 min to facilitate longer procedures or surgery. Anesthesia was antagonized with atipamezole (0.05-0.06 mg/kg) and naltrexone (0.1 mg/kg) in seven events, with the addition of flumazenil (0.0002-0.002 mg/kg) in six events. The antagonists were administered by i.m. injection 42-149 min after administration of the induction agents. All sea lions recovered to mild sedation within 4-17 min after administration of the antagonists.     

Vitamin A deficiency and hepatic retinol levels in sea otters, Enhydra lutris

Vitamin A deficiency has rarely been reported in captive or free-ranging wildlife species. Necropsy findings in two captively housed southern sea otters (Enhydra lutris nereis) included irregular thickening of the calvaria characterized by diffuse hyperostoses on the internal surface. One animal also had moderate squamous metaplasia of the seromucinous glands of the nose. There was no measurable retinol in the liver of either sea otter. For comparison, hepatic retinol concentration was determined for 23 deceased free-ranging southern and northern (Enhydra lutris kenyoni) sea otters from California and Alaska. Free-ranging otters were found to have similar hepatic retinol concentrations (316 +/- 245 mg/kg wet weight) regardless of their location and subspecies. All of these values were significantly higher than the levels in the affected animals. Consumption of a diet with very low vitamin A concentrations and noncompliance in daily supplementation are hypothesized as the causes of vitamin A deficiency in these two sea otters.     

Naloxone reversal of an overdose of a novel, long-acting transdermal fentanyl solution in laboratory Beagles

Opioid overdose in dogs is manifested by clinical signs such as excessive sedation, bradycardia, and hypothermia. The ability of two different intramuscular (i.m.) naloxone reversal regimens to reverse the opioid-induced effects of a fivefold overdose of long-acting transdermal fentanyl solution was evaluated in dogs. Twenty-four healthy Beagles were administered a single 13 mg/kg dose (fivefold overdose) of transdermal fentanyl solution and randomized to two naloxone reversal regimen treatment groups, hourly administration for 8 h of 40 (n = 8) or 160 μg/kg i.m. (n = 16). All dogs were sedated and had reduced body temperatures and heart rates (HRs) prior to naloxone administration. Both dosage regimens significantly reduced sedation (P < 0.001), and the 160 μg/kg naloxone regimen resulted in a nearly threefold lower odds of sedation than that of the 40 μg/kg i.m. naloxone regimen (P < 0.05). Additionally, naloxone significantly increased the mean body temperatures and HR (P < 0.001), although the 160 μg/kg regimen increased body temperature and HR more (P < 0.05). However, the narcotic side effects of fentanyl returned within 1-3 h following termination of the naloxone dosage regimens. The opioid-induced effects of an overdose of transdermal fentanyl solution can be safely and effectively reversed by either 40 or 160 μg/kg i.m. naloxone administered at hourly intervals.     

Anaesthesia with midazolam/medetomidine/fentanyl in chinchillas (Chinchilla lanigera) compared to anaesthesia with xylazine/ketamine and medetomidine/ketamine

We studied four different drug regimes for anaesthetic management in chinchillas and evaluated and compared their cardiovascular and respiratory effects. In this randomized, cross-over experimental study, seven adult chinchillas, five females, two males [515 +/- 70 (SD) g] were randomly assigned to one of the following groups: group 1 [midazolam, medetomidine and fentanyl (MMF), flumazenil, atipamezole and naloxone (FAN); MMF-FAN] received 1.0 mg/kg midazolam, 0.05 mg/kg medetomidine and 0.02 mg/kg fentanyl i.m., and for reversal 0.1 mg/kg flumazenil, 0.5 mg/kg atipamezole and 0.05 mg/kg naloxone s.c. after 45 min; group 2 (MMF) 1.0 mg/kg midazolam, 0.05 mg/kg medetomidine and 0.02 mg/kg fentanyl i.m.; group 3 [xylazine/ketamine (X/K)] 2.0 mg/kg xylazine and 40.0 mg/kg ketamine i.m.; and group 4 [medetomidine/ketamine (M/K)] 0.06 mg/kg medetomidine and 5.0 mg/kg ketamine i.m. Reflexes were judged to determine anaesthetic stages and planes. Anaesthesia with X/K and M/K was associated with a prolonged surgical tolerance and recovery period. By reversing MMF, recovery period was significantly shortened (5 +/- 1.3 min versus 40 +/- 10.3 min in MMF without FAN, 73 +/- 15.0 min in X/K, and 31 +/- 8.5 min in M/K). Without reversal, MMF produced anaesthesia lasting 109 +/- 16.3 min. All combinations decreased respiratory and heart rate but compared with X/K and M/K, respiratory and cardiovascular complications were less in the MMF groups. Focussing on the clinical relevance of the tested combinations, completely reversible anaesthesia showed two major advantages: anaesthesia can be antagonized in case of emergency and routinely shortens recovery. In small animals particularly these advantages lead to less complications and discomfort and thus often can be lifesaving. As all analgesic components (medetomidine and fentanyl) are reversed, postoperative analgesia should be provided before reversal of anaesthesia.     

Appetite-modulating drugs in dwarf goats, with special emphasis on benzodiazepine-induced hyperphagia and its antagonism by flumazenil and R° 15–3505

In dwarf goats fasted for 2 h, i.v. administration of the benzodiazepine (BZ) agonists diazepam (60 micrograms/kg), brotizolam (2 and 4 micrograms/kg) and climazolam (100 micrograms/kg) induced hyperphagic effects, whereas i.v. injections of the BZ-antagonist flumazenil (R degrees 15-1788; 0.5 mg/kg), the anthelmintic ivermectin (0.1 mg/kg), the 5-HT2 antagonist ritanserine (0.1 mg/kg), ACTH (10 micrograms/kg) and prednisolone (1 mg/kg) were inactive in a 30-min feeding test. Both the BZ-antagonist R degrees 15-3505 (greater than or equal to 0.1 mg/kg) and the opiate receptor antagonist naloxone (0.1 mg/kg) had anorectic effects in dwarf goats given 30 min access to a palatable pelleted concentrate. The hyperphagic effects of climazolam and brotizolam were not antagonized by flumazenil, whereas similar doses of this drug completely reversed muscle incoordination and ataxia induced by much higher doses of these BZ-agonists. In the combination experiments with naloxone and BZ-agonists, naloxone antagonized the hyperphagic effects of both diazepam and brotizolam. Similarly, in the diazepam-R degrees 15-3505 study, there was a significant effect of diazepam and a significant inhibition of this effect by R degrees 15-3505 (50 micrograms/kg). In the diazepam-ivermectin combination experiment no evidence for drug potentiation was found. These results and the mode of action of the above mentioned drugs are discussed in relation to feeding behaviour.     

Intrathecal morphine overdose in a dog

CASE DESCRIPTION: A healthy 6-year-old 28.5-kg (62.7-lb) spayed female Boxer undergoing surgical repair of a ruptured cranial cruciate ligament was inadvertently administered an overdose of morphine (1.3 mg/kg [0.59 mg/lb]) via subarachnoid injection. CLINICAL FINDINGS: 50 minutes after administration of the overdose, mild multifocal myoclonic contractions became apparent at the level of the tail; the contractions migrated cranially and progressively increased in intensity and frequency during completion of the surgery. TREATMENT AND OUTCOME: The myoclonic contractions were refractory to treatment with midazolam, naloxone, phenobarbital, and pentobarbital; only atracurium (0.1 mg/kg [0.045 mg/lb], IV) was effective in controlling the movements. The dog developed hypertension, dysphoria, hyperthermia, and hypercapnia. The dog remained anesthetized and ventilated mechanically; treatments included continuous rate IV infusions of propofol (1 mg/kg/h [0.45 mg/lb/h]), diazepam (0.25 mg/kg/h [0.11 mg/lb/h]), atracurium (0.1 to 0.3 mg/kg/h [0.045 to 0.14 mg/lb/h]), and naloxone (0.02 mg/kg/h [0.009 mg/lb/h]). Twenty-two hours after the overdose, the myoclonus was no longer present, and the dog was able to ventilate without mechanical assistance. The dog remained sedated until 60 hours after the overdose, at which time its mentation improved, including recognition of caregivers and response to voice commands. No neurologic abnormalities were detectable at discharge (approx 68 hours after the overdose) or at a recheck evaluation 1 week later. CLINICAL RELEVANCE: Although intrathecal administration of an overdose of morphine can be associated with major and potentially fatal complications, it is possible that affected dogs can completely recover with immediate treatment and extensive supportive care.     

Effects of naloxone in treating hemorrhagic shock in dogs with maintained baroreceptor responsiveness

The efficacy of treating hemorrhagic shock with naloxone in conjunction with fluids, compared with fluid therapy alone, was studied. Previously instrumented dogs were anesthetized with 0.04 mg of fentanyl/kg + 2.2 mg of droperidol/kg and pentobarbital sodium (to effect). Blood was withdrawn from each animal to achieve and maintain a mean arterial blood pressure of 40 to 50 mm of Hg for the first 2 hours of the experiment (t = 0 to 120 minutes). At t = 120 minutes, IV fluid administration was begun (all dogs) and continued for 1 hour (lactated Ringer's solution at a dosage of 70 ml/kg/hr). Hypothermia was corrected. Control dogs were given no other treatment. Dogs in the naloxone plus fluids group were given an IV bolus of naloxone (1 mg/kg) at t = 120 minutes and 1 mg of naloxone/kg/hr in the fluids from t = 120 to t = 180 minutes. Treatment (either naloxone plus fluids or fluids alone) was stopped at t = 180 minutes, and measuring of response was continued for an additional hour (posttherapeutic period). Significant differences were not seen in mean arterial pressures, left ventricular peak systolic pressures, dP/dt max, time constant T (a measure of left ventricular elasticity), and mean pulmonary arterial pressures between the dogs given naloxone and fluid therapy and those given fluid therapy alone. All dogs in both groups survived the procedure.     

Use of naloxone to reverse carfentanil citrate-induced hypoxemia and cardiopulmonary depression in Rocky Mountain wapiti (Cervus elaphus nelsoni).

With the use of a crossover study design, we investigated the respiratory and cardiovascular effects of naloxone administration in eight healthy Rocky Mountain wapiti (Cervus elaphus nelsoni) anesthetized with carfentanil (10 microg/kg i.m.) and xylazine (0.1 mg/kg). Anesthetized animals showed profound hypoxemia with mild hypercapnia, tachycardia, hypertension, and acidosis prior to naloxone administration. After monitoring equipment was placed, animals were administered either naloxone (2 microg/microg carfentanil i.v.) or an equivalent volume of normal saline. Mean values for PaO2, PaCO2, heart rate, and respiratory rate were significantly different between naloxone- and saline-treated groups, but mean blood pressure, hematocrit, and serum electrolyte concentrations were not. Mean PaO2 was 23.0 +/- 4.1 mm Hg prior to administration of naloxone or saline and increased to 50.2 +/- 7.3 mm Hg after naloxone administration. Mean PaO2 of saline-treated animals did not change significantly. Electrocardiograms of three saline-treated animals suggested myocardial hypoxia. Hypoxemia appeared to be caused by respiratory depression, hemodynamic alterations, and lateral recumbency. All but one animal remained anesthetized after naloxone administration. Anesthesia in all animals was reversed in < or = 4 min with naltrexone (100 mg/mg carfentanil i.v. s.c.) and yohimbine (0.1 mg/kg i.v.). One bolus of naloxone improved oxygenation in carfentanil-xylazine-anesthetized wapiti.     

Effect of transdermally administered fentanyl on the minimum alveolar concentration of isoflurane in cats

OBJECTIVE: To determine the effect of two doses of fentanyl, administered transdermally, on the minimum alveolar concentration (MAC) of isoflurane in cats. STUDY DESIGN: Prospective, randomized study. ANIMALS: Five healthy, spayed, female cats. METHODS: Each cat was studied thrice with at least 2 weeks between each study. In study 1, the baseline isoflurane MAC was determined in triplicate for each cat. In studies 2 and 3, isoflurane MAC was determined 24 hours after placement of either a 25 or 50 microg hour(-1) fentanyl patch. In each MAC study, cats were instrumented to allow collection of arterial blood and measurement of arterial blood pressure. Twenty-four hours prior to studies 2 and 3, a catheter was placed and secured in the jugular vein and either a 25 or 50 microg hour(-1) fentanyl patch was placed in random order on the left thorax. Blood samples for plasma fentanyl determination were collected prior to patch placement and at regular intervals up to 144 hours. After determination of MAC in studies 2 and 3, naloxone was administered as a bolus dose (0.1 mg kg(-1)) followed by an infusion (1 mg kg(-1) hour(-1)) and MAC redetermined. RESULTS: The baseline isoflurane MAC was 1.51 +/- 0.21% (mean +/- SD). Fentanyl (25 and 50 micro g hour(-1)) administered transdermally significantly reduced MAC to 1.25 +/- 0.26 and 1.22 +/- 0.16%, respectively. These MAC reductions were not significantly different from each other. Isoflurane MAC determined during administration of fentanyl 25 micro g hour(-1) and naloxone (1.44 +/- 0.16%) and fentanyl 50 micro g hour(-1) and naloxone (1.51 +/- 0.19%) was not significantly different from baseline MAC (1.51 +/- 0.21%). CONCLUSIONS AND CLINICAL RELEVANCE: Fentanyl patches are placed to provide long-lasting analgesia. In order to be effective postoperatively, fentanyl patches must be placed prior to surgery. Plasma fentanyl concentrations achieved intraoperatively decrease the need for potent inhalant anesthetics in cats.     

Standing sedation in African elephants (Loxodonta africana) using detomidine-butorphanol combinations.

Standing sedation was provided for 14 clinical procedures in three African elephants (Loxodonta africana) managed by combined protected and modified-protected contact and trained through operant conditioning. An initial hand-injection of detomidine hydrochloride and butorphanol tartrate at a ratio of 1:1 on a microg:microg basis was administered intramuscularly, with a dosage range of 50-70 mg (12.9-19.7 microg/kg) for each drug. The initial injection resulted in adequate sedation for initiation and completion of eight procedures, whereas supplemental doses were required for the remaining procedures. The dosage range for the supplemental injections of each drug was 4.0-7.3 microg/kg. Initial effect was noted within 3.0-25 min (mean = 11.6 min, SD +/- 5.9 min), with maximal effect occurring at 25-30 min for those procedures not requiring supplementation. In all but one procedure, this effect was maintained until the end of the procedure, which ranged from 47 to 98 min (mean = 74.7 min, SD +/- 18.8 min). No cardiac or respiratory depression was appreciated. Recovery after administration of reversal agents was rapid and complete, ranging from 2 to 20 min (mean = 9.0 min, SD +/- 7.0 min). On the basis of the authors' experience, recommended dosage ranges for reversal agents would be intravenous yohimbine (73.4-98.5 microg/kg), intravenous naltrexone (48.9-98.5 microg/kg), and intramuscular naltrexone (73.4-98.5 microg/kg). Approximately one-third to one-half of the total naltrexone dose should be administered intravenously. Mild adverse side effects limited to the gastrointestinal tract were observed in association with five procedures including abdominal distention with or without transient anorexia. Administration of reversal agents, encouraging exercise and water consumption, and administration of flunixin meglumine were helpful in the resolution of signs. In addition to gastrointestinal signs, slight ataxia was observed before initiation of surgical stimulation during one procedure in which 19.7 microg/kg of each drug was administered. On the basis of the procedures that did not require supplementation to initiate treatment and taking into consideration the potential for ataxia at higher doses, a starting dosage range of 14.7-16.2 microg/kg of both detomidine and butorphanol in a ratio of 1:1 on a microg:microg basis administered i.m. simultaneously is recommended.     

How Messaging Shapes Attitudes toward Sea Otters as a Species at Risk

To address the drivers of biodiversity loss, conservation efforts must attend to public attitudes toward endangered species. Using sea otters as a species at risk, we examined how messaging shapes people’s attitudes toward this species. Participants viewed a message about sea otters that was either positive (sea otters as keystone species), negative (resource conflict with local fishermen), or neutral (biological facts). The impact of the message on people’s attitudes was measured using Kellert’s typology of basic attitudes toward wildlife. We found that the negative message promoted people’s interests in the practical value of sea otters (utilitarian-consumption attitudes), their habitats (utilitarian-habitat attitudes), and control over sea otters (dominionistic attitudes), even though the negative message was perceived as less convincing and believable than positive or neutral messages. The positive message decreased utilitarian-consumption attitudes, and the neutral message decreased utilitarian-habitat attitudes. Our findings suggested that messaging can influence public attitudes toward wildlife.     

Effects of lidocaine constant rate infusion on sevoflurane requirement, autonomic responses, and postoperative analgesia in dogs undergoing ovariectomy under opioid-based balanced anesthesia

The effects of constant rate infusion (CRI) of lidocaine on sevoflurane (SEVO) requirements, autonomic responses to noxious stimulation, and postoperative pain relief were evaluated in dogs undergoing opioid-based balanced anesthesia. Twenty-four dogs scheduled for elective ovariectomy were randomly assigned to one of four groups: BC, receiving buprenorphine without lidocaine; FC, receiving fentanyl without lidocaine; BL, receiving buprenorphine and lidocaine; FL, receiving fentanyl and lidocaine. Dogs were anesthetized with intravenous (IV) diazepam and ketamine and anesthesia maintained with SEVO in oxygen/air. Lidocaine (2mg/kg plus 50μg/kg/min) or saline were infused in groups BL/FL and BC/FC, respectively. After initiation of lidocaine or saline CRI IV buprenorphine (0.02mg/kg) or fentanyl (4μg/kg plus 8μg/kg/h CRI) were administered IV in BC/BL and FC/FL, respectively. Respiratory and hemodynamic variables, drug plasma concentrations, and end-tidal SEVO concentrations (E'SEVO) were measured. Behaviors and pain scores were subjectively assessed 1 and 2h post-extubation. Lidocaine CRI produced median drug plasma concentrations <0.4μg/mL during peak surgical stimulation. Lidocaine produced a 14% decrease in E'SEVO in the BL (P<0.01) but none in the FL group and no change in cardio-pulmonary responses to surgery or postoperative behaviors and pain scores in any group. Thus, depending on the opioid used, supplementing opioid-based balanced anesthesia with lidocaine (50μg/kg/min) may not have any or only a minor impact on anesthetic outcome in terms of total anesthetic dose, autonomic responses to visceral nociception, and postoperative analgesia.     

Testosterone and luteinizing hormone responses to naloxone help predict sexual performance in rams

The first objective of this study was to determine whether LH and testosterone respond differently to a naloxone injection in relation to varying sexual performance in rams. If differences occurred, the second objective was to determine whether differences would predict variation in sexual performance. From a group of 1.5- to 3-yr-old rams, 20 sexually active and 39 sexually inactive rams were selected based on previously observed sexual behavior with estrual ewes. Each ram was exposed to three estrual ewes for 18 30-min sexual performance tests, and those found to be inactive were given two 30-min sexual partner preference tests. The final distribution was 28 sexually active, 22 inactive, and nine male-oriented rams. Rams were treated with 1.5 mg of naloxone/kg BW in December of Year 1 and again with either 0.75 or 1.5 mg of naloxone/kg BW in November of Year 2. Plasma concentrations of LH and testosterone were evaluated with mixed model analyses for repeated measures separately for each year to coincide with logistic procedures for modeling the probability that rams were sexually active. For Year 1, a sexual activity x age x time interaction for LH after naloxone was observed (P < 0.03). For testosterone, there was a sexual activity x time interaction (P < 0.03), with a similar, early increase for sexually active female-and male-oriented rams compared with a delayed, minimal increase for inactive rams. For Year 2, when all rams were over 2.5 yr of age, a sexual activity x time interaction for both LH and testosterone (P < 0.02) seemed more related to an earlier increase of both hormones for sexually active rams than the increase observed for inactive rams. In addition, sexually active rams had a greater increase in testosterone than inactive rams. No significant difference was observed between 0.75 and 1.50 mg of naloxone/kg BW. Testosterone and LH were used as explanatory variables and sexual activity was used as the response variable in logistic procedures. In Year 1, greatest prediction accuracy was 73.5% using testosterone at 60 min after naloxone injection. In Year 2, the greatest prediction accuracy was 85% using LH at 15 min multiplied by testosterone at 60 min after naloxone. Test repeatability for both years on the same rams was 76%. In conclusion, pattern and magnitude of naloxone-induced changes in endocrine function may facilitate identification of sexually active and inactive rams during the breeding season. Prediction accuracy of the naloxone-based test was 69 to 85%.     

Investigation into the use of narcotic antagonists in the treatment of a stereotypic behavior pattern (crib-biting) in the horse

Crib-biting in horses is a repetitive behavior pattern which may involve the activation of both narcotic receptors and dopamine receptors in the CNS. Crib-biting frequency, determined in 7 nontreated horses under controlled conditions, was usually linear for many hours and ranged from 0.3 to 14.9 bites/min. Intravenous or IM injections of narcotic antagonists decreased these rates to almost zero by about 20 minutes after the injection was given. The duration of the response to a single injection ranged from 20 minutes for naloxone to 4 hours or more for nalmefene and diprenorphine. Effective doses were 0.02 to 0.04 mg of naloxone/kg, 0.04 mg of naltrexone/kg, 0.08 mg of nalmefene/kg, and 0.02 to 0.03 mg of diprenorphine/kg. Crib-biting could be prevented completely for up to a week by continuous infusion of 5 to 10 mg of nalmefene/hr. Crib-biting resumed when the infusion was discontinued, and plasma nalmefene concentrations decreased to below 5 ng/ml. Doses of nalmefene as large as 0.4 mg/kg, IV, produced only minor side effects. These side effects included some passage of semifluid fecal material, intermittent penile relaxation, and mild sedation. Treated horses responded normally to external stimuli, retained their appetites, and performed appropriately when ridden. Sedation wore off during the course of prolonged infusions. Narcotic antagonists may provide a novel and effective treatment of stereotypic behavior disorders.     

Total intravenous anesthesia in greyhounds: pharmacokinetics of propofol and fentanyl--a preliminary study

OBJECTIVE: To evaluate concomitant propofol and fentanyl infusions as an anesthetic regime, in Greyhounds. ANIMALS: Eight clinically normal Greyhounds (four male, four female) weighing 25.58 +/- 3.38 kg. DESIGN: Prospective experimental study. METHODS: Dogs were premedicated with acepromazine (0.05 mg/kg) by intramuscular (i.m.) injection. Forty five minutes later anesthesia was induced with a bolus of propofol (4 mg/kg) by intravenous (i.v.) injection and a propofol infusion was begun (time = 0). Five minutes after induction of anesthesia, fentanyl (2 microg/kg) and atropine (40 microg/kg) were administered i.v. and a fentanyl infusion begun. Propofol infusion (0.2 to 0.4 mg/kg/min) lasted for 90 minutes and fentanyl infusion (0.1 to 0.5 microg/kg/min) for 70 minutes. Heart rate, blood pressure, respiratory rate, end-tidal carbon dioxide, body temperature, and depth of anesthesia were recorded. The quality of anesthesia, times to return of spontaneous ventilation, extubation, head lift, and standing were also recorded. Blood samples were collected for propofol and fentanyl analysis at varying times before, during and after anesthesia. RESULTS: Mean heart rate of all dogs varied from 52 to 140 beats/min during the infusion. During the same time period, mean blood pressure ranged from 69 to 100 mm Hg. On clinical assessment, all dogs appeared to be in light surgical anesthesia. Mean times (+/- SEM), after termination of the propofol infusion, to return of spontaneous ventilation, extubation, head lift and standing for all dogs were 26 +/- 7, 30 +/- 7, 59 +/- 12, and 105 +/- 13 minutes, respectively. Five out of eight dogs either whined or paddled their forelimbs in recovery. Whole blood concentration of propofol for all eight dogs ranged from 1.21 to 6.77 microg/mL during the infusion period. Mean residence time (MRTinf) for propofol was 104.7 +/- 6.0 minutes, mean body clearance (Clb) was 53.35 +/- 0.005 mL/kg/min, and volume of distribution at steady state (Vdss) was 3.27 +/- 0.49 L/kg. Plasma concentration of fentanyl for seven dogs during the infusion varied from 1.22 to 4.54 ng/mL. Spontaneous ventilation returned when plasma fentanyl levels were >0.77 and <1.17 ng/mL. MRTinf for fentanyl was 111.3 +/- 5.7 minutes. Mean body clearance was 29.1 +/- 2.2 mL/kg/min and Vdss was 2.21 +/- 0.19 L/kg. CONCLUSION AND CLINICAL RELEVANCE: In Greyhounds which were not undergoing any surgical stimulation, total intravenous anesthesia maintained with propofol and fentanyl infusions induced satisfactory anesthesia, provided atropine was given to counteract bradycardia. Despite some unsatisfactory recoveries the technique is worth investigating further for clinical cases, in this breed and in mixed breed dogs.     

Antagonistic effects of naloxone in analgesia and neuroleptanalgesia in the dog

Antagonistic effect of naloxone was tested in two kinds of total anesthesia. In one group the preparation was tested in ten experimental dogs with neuroleptanalgesia induced by the simultaneous intramuscular application of chlorpromazine (3 mg/kg) and piritramide (4 mg/kg). After 60 minutes naloxone was applied i. m. at a dose of 0.2-0.4 mg pro toto to reverse the anesthetic effect. In another group of 15 dogs - clinical patients - the effect of naloxone was evaluated in analgesia induced by i. m. application of piritramide at a dose of 3 mg per kg with atropine premedication (0.05 mg per kg). After a surgical operation, lasting in particular cases 20-45 minutes, the same dose of naloxone was applied i. m. as in the first group to reverse the anesthetic effect. In both groups of animals naloxone application caused a reverse of the anesthetic effect of piritramide and in the first group a statistically significant reverse of the inhibition of breathing and heart action.     

Anesthesia in the Richardson's ground squirrel: comparison of ketamine, ketamine and xylazine, droperidol and fentanyl, and sodium pentobarbital

A combination of ketamine and xylazine (88.9 mg of ketamine/ml and 11.1 mg of xylazine/ml) given IM (85.5 +/- 3.4 mg of ketamine/kg of body weight and 10.6 +/- 0.5 mg of xylazine/kg) or subcutaneously (85.6 +/- 4.0 mg of ketamine/kg and 10.7 +/- 0.7 mg of xylazine/kg) induced effective surgical anesthesia for 20 to 30 minutes in Richardson's ground squirrels. Use of ketamine alone (86 +/- 7 mg/kg, IM), a droperidol and fentanyl combination (2.6 +/- 0.4 mg of droperidol/kg and 52 +/- 8 micrograms of fentanyl/kg, IM), or sodium pentobarbital (50 +/- 2 mg/kg, intraperitoneally) did not induce surgical anesthesia, but did induce depressed respiratory rates in the squirrels.