RABBITS AND FERRETS IN FOCUS

Transcription

1 Vet Times The website for the veterinary profession RABBITS AND FERRETS IN FOCUS Author : LESA LONGLEY Categories : Vets Date : May 19, 2008 LESA LONGLEY reports on the research findings and treatment suggestions raised by two international speakers THE rabbits and ferrets stream was spread over three days of the BSAVA Congress. The sessions were well attended, proving the importance of, and interest in, these species in general practice. The speakers covered a broad selection of subjects, describing diseases as well as techniques and treatment. Rabbits Marla Lichtenberger is an emergency and critical care specialist and an internationally renowned speaker on critical care in small animals, including exotic species. Her masterclass, entitled The critically ill rabbit: how we can save them was popular, as were her later presentations on gastrointestinal emergencies, anaesthesia, analgesia and monitoring, acute renal failure, shock and fluid therapy. She also hosted an interactive session. Shock Dr Lichtenberger described how rabbits commonly suffer from hypovolaemic shock due to a variety of conditions. Unlike dogs, but similar to cats, they appear to skip the compensatory phase of shock, as simultaneous vagal and sympathetic stimulation produces the decompensatory phase with 1 / 8

2 bradycardia (heart rate less than 180bpm), hypothermia (less than 36 C) and hypotension (less than 90mmHg). Fluids A protocol for the treatment of shock was outlined, which included reperfusion with administration of a slow (between five to 10 minutes) intravenous bolus of hypertonic saline (3ml/kg) with hetastarch (3ml/kg). Hypertonic saline results in a transient expansion of the intravascular space, and the addition of hetastarch helps retain fluid there. Aggressive warming is performed, preferably using forced-air blankets. Dr Lichtenberger recommends repeating crystalloid (such as lactated Ringer s solution) and hetastarch boluses two to three times (if necessary) until normal systolic blood pressure is attained. In refractory cases, blood transfusions or a haemoglobin solution (such as Oxyglobin at 2ml/kg slowly) can be administered to improve oxygen-carrying capacity. Once a rectal temperature of 36 C is attained, crystalloids are administered at maintenance rate (3ml/kg/hr to 4ml/kg/hr). Rehydration also requires consideration of the degree of dehydration in the patient, and acute and chronic fluid losses. External (using blankets or heat pads) and core (by warming intravenous fluids) heating is continued until normothermia is achieved (more than 38 C; the normal range is 38.5 C to 40 C). Initial blood samples for packed-cell volume, total protein, blood glucose and azotaemia are useful baseline parameters. Fluid administration often corrects stress hyperglycaemia. Urea may be elevated with renal failure. Early work has shown that lactate may be a marker for sepsis and gastrointestinal disease. Analgesics and anaesthetics Many ill rabbits presented to veterinary practices are anxious. An initial dose of butorphanol (0.4mg/kg to 0.8mg/kg) and midazolam (0.25mg/kg to 0.5mg/kg) was suggested to calm patients, with later administration of buprenorphine (0.04mg/kg to 0.06mg/kg) to provide further analgesia. Buprenorphine will be absorbed in rabbits if applied to oral mucous membranes (0.06mg/kg to 0.08mg/kg). Dr Lichtenberger recommended the use of multimodal analgesia, and described the use of various local anaesthetics (such as lidocaine and bupivacaine), NSAIDs (such as meloxicam) and opioids (such as butorphanol, buprenorphine, morphine, fentanyl and tramadol), including the use of continuous rate infusions (CRI) for analgesia provision. Local nerve blocks were described for use in dental procedures. These included infraorbital, maxillary, mandibular and mental blocks, by using a lidocaine and bupivacaine mixture. Caution was expressed over the use of NSAIDs in anaesthetised patients, with administration 2 / 8

3 towards the end of procedures to minimise cardiovascular effects, and also over high doses of alpha-2 agonists (although microdoses were recommended as part of sedative protocols). Dr Lichtenberger s preferred anaesthetic regime for dental procedures was etomidate, midazolam and meloxicam, with the addition of a fentanyl (0.005mg/ kg/hr) and/or ketamine (0.5mg/ kg/hr) with a CRI and isoflurane (one to two per cent) for more extensive procedures. Where more invasive procedures, such as exploratory coeliotomy, were planned more emphasis was placed on provision of analgesia. Preoperative fentanyl (10µg/kg) is administered before induction with alfaxalone or etomidate and midazolam. Anaesthesia is maintained using a fentanyl/ketamine CRI and isoflurane (one to two per cent), possibly with additional analgesia from morphine (0.1mg/kg to 0.2mg/kg, plus or minus bupivacaine 0.1mg/kg) epidurally. Monitoring is incredibly important for these patients, particularly with regard to blood pressure (using a small cuff on the forelimb, as in cats). If hypotension is noted, gaseous anaesthetics are reduced, crystalloids are administered (15ml/kg bolus), and consideration given to the use of hetastarch and hypertonic saline as described above. Possible blood loss should be identified and corrected, and correction may require a haemoglobin solution and/or a blood transfusion. Resuscitation Monitoring equipment is vital to detecting early warning signs of patient deterioration. An ECG or audible Doppler may detect bradycardia before respiratory and cardiac arrest. Dr Lichtenberger uses this warning to administer glycopyrrolate intravenously, followed by doxapram and intermittent positive pressure ventilation if respiratory arrest occurs. Vasopressin (0.8 units/kg) is recommended in cases of asystole. Acute renal failure Dr Lichtenberger outlined possible causes of renal failure in rabbits such as hypovolaemia, urolithiasis and Encephalitozoon cuniculi infection. Investigation should include urine analysis, haematology and/ or biochemistry, and ultrasound. Initial treatment involves reperfusion and rehydration. Once the patient is rehydrated and urine output is more than 2ml/kg/hr (monitored by weighing incontinence pads used in the kennel), diuresis is instigated with further fluid therapy until urine output is normal and azotaemia has been corrected. Fluids are tapered to allow correction of medullary washout, and nutritional support is often required. Supplemental nutrition 3 / 8

4 Assisted feeding is often required, as anorexic rabbits rapidly succumb to gastrointestinal disease, including gastric stasis and hepatic lipidosis. After reperfusion, rehydration and analgesia, Dr Lichtenberger routinely places nasogastric feeding tubes in patients that will not readily accept assisted feeding by syringe. For most rabbits, a 5-8Fr tube can be used. The positioning can be checked using radiography. Fluid or fluid diets (such as Oxbow Critical Care Fine Grind) can be administered via feeding tubes. Flush the tube with water before and after usage, along with administration of prokinetics (such as ranitidine 0.5mg/kg q12h). Ferrets Nico Schoemaker is an associate professor at the division of avian and exotic animal medicine at Utrecht University, in the Netherlands. He is commonly known as Mr Ferret, due to his immense knowledge of the species (his PhD thesis was on adrenal gland disease in the ferret). Dr Schoemaker s presentations covered What every veterinarian should know about ferret medicine and approaches to ferrets with alopaecia and hindlimb weakness. He also made a special presentation on the use of a deslorelin implant as an alternative to surgical castration in ferrets. Husbandry and healthcare Dr Schoemaker s first presentation outlined the history of ferrets in captivity, including their guises as pets and working animals. He described ferret restraint, clinical examination and various techniques for investigation of disease. Phlebotomy can be difficult in ferrets, and Dr Schoemaker recommended either conscious sampling from the jugular vein or isoflurane anaesthesia for accessing the cranial vena cava. For more prolonged procedures, Dr Schoemaker uses either medetomidine (80µg/kg to 100µg/kg, reversing with atipamezole at 200µg/kg to 250µg/kg) and ketamine (5mg/ kg) or isoflurane (inducing with four per cent and maintaining on two per cent). For surgery, a premedication of medetomidine (100µg/kg) allows intravenous catheter placement in the cephalic vein, before induction with propofol (1mg/kg to 3mg/ kg), intubation (2mm to 2.5mm endotracheal tube) and maintenance on isoflurane (one to two per cent). Anaesthesia monitoring equipment includes an ECG, capnograph and thermometer. Viral diseases that ferrets are susceptible to include canine distemper, influenza and Aleutian disease. Annual vaccination against distemper is recommended, although there is currently no licensed vaccine for ferrets. Other common conditions that were discussed included lymphoma, splenomegaly (with several aetiologies, but usually not of clinical importance) and cardiomyopathy. Alopaecia 4 / 8

5 Infectious aetiologies of alopaecia include dermatophytosis, mange (Demodex), and bacterial dermatitis. Non-infectious causes include seasonal alopaecia and food intolerance. Hormonal disease includes persistent oestrus and remnant ovaries in jills, Sertoli cell tumours in hobs, hyperadrenocorticism (HAC) very common in both sexes and hypothyroidism, which is rare. Up to 75 per cent of neutered ferrets develop HAC. Clinical signs associated with the disease were described in the presentation, and include symmetrical alopaecia, stranguria (due to prostate hypertrophy and cysts), pruritus (unknown origin), a return of sexual behaviour in neutered animals and a swollen vulva in neutered jills. Diagnosis is mainly based on the symptoms seen and ultrasound detection of abnormal adrenal glands, although other investigations may include abdominal palpation and hormone analysis. Levels of androstenedione, oestradial and 17-hydroxyprogesterone are commonly elevated, but do not differentiate HAC from an active remnant ovary. Historically, adrenalectomy has been the treatment of choice for HAC, but work on depot GnRH agonists (such as leuprolide acetate and deslorelin) has shown promise. Hindlimb weakness Differential diagnoses for hindlimb weakness in the ferret include neuromuscular disease, but there are also systemic circulatory causes, including insulinoma and cardiac disease. Dr Schoemaker emphasised the need for a good history to aid differentiation, along with a complete physical examination (including neurological assessment). Blood glucose should be measured at least four hours after feeding. Haematology and biochemistry are useful to investigate metabolic disease. Imaging techniques, such as radiography and ultrasound, may be useful, as can cerebrospinal fluid analysis. Treatment of insulinoma may be by surgical resection or medical therapy. Dr Schoemaker advises diazoxide as the first line of medical management (starting dose 5mg/kg PO q12h, with titrating based on blood glucose levels), although prednisolone is a commonly used alternative. Aleutian disease is rare. Common clinical signs include chronic wasting, hindlimb paresis and/or paralysis and urine and faecal incontinence. Hypergammaglobulinaemia may be seen, and a positive antibody test or ELISA supports the diagnosis. Deslorelin implants Although the exact aetiology of HAC is not known, one hypothesis for the high incidence in neutered ferrets is that LH hormone levels stimulate tumour production in the adrenal glands. Dr Schoemaker proposed several alternatives to the surgical neutering of ferrets. Although proligestone (50mg/kg SC) is commonly used in the UK, some animals require three injections in one season. Side effects may include pseudopregnancy and aggression. Dr Schoemaker has 5 / 8

6 performed studies using deslorelin implants to assess the effect on the reproductive system. A small study in 20 intact male ferrets showed a reduction in testosterone, testicular volume, the amount of odour produced and aggressive and sexual behaviour. Histology on testes from the group receiving deslorelin (seven animals) showed no sperm production was present. A larger study (220 privately owned ferrets, comprising both hobs and jills) with implants has shown some hobs still have aggressive or sexual behaviour, although testosterone levels were below the assay detection limit. Some jills came into oestrus transiently and some developed pseudopregnancy. The implant appears to be effective for at least one-and-a-half years and seems to be a suitable alternative to surgical neutering in ferrets. However, further research is required to evaluate whether the use of medical neutering will reduce the incidence of HAC. Summary Other exotic animals discussed at BSAVA included a pre-congress day organised by the British Veterinary Zoological Society. This covered the basics of veterinary medicine and surgery in a wide range of species, including fish, primates, macropods and wildlife (case studies, capture and anaesthesia). There was also an avian stream in the nursing programme. This included presentations on avian nursing (Donna Brown), anaesthesia (Romain Pizzi), radiography (Mark Evans) and triage (Steve Smith). Both Dr Lichtenberger and Dr Schoemaker are accomplished speakers and audience members in the BSAVA rabbits and ferrets stream were entertained as well as enlightened. Dr Lichtenberger and Dr Schoemaker have an evident passion for rabbits and ferrets, ensuring everyone s attention throughout. Along with research insights into rabbits and ferrets, they shared their experiences in current treatments of these animals. We left with new knowledge of techniques, along with a better understanding of disease and veterinary care in these species. Apart from isoflurane (which is licensed for use in small mammals), drugs discussed in this article are not licensed for use in these species. References are available on request to the editor. 6 / 8

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8 Powered by TCPDF ( Audiences were entertained and enlightened with presentations by Nico Schoemaker on ferrets and Marla Lichtenberger on rabbits. 8 / 8