Management of Rabbits
Management of rabbits for meat, fur, or wool production is quite different from maintenance of a pet or house rabbit. The American Rabbit Breeders Association (www.arba.net) provides guidance for both production and pet rabbit care. The House Rabbit Society (www.rabbit.org) is another resource regarding pet rabbit care.
Proper handling and restraint is important. Rabbits have powerful hindlimbs, which can kick out and lead to broken backs. Rabbits should never be held by the ears; they should be scruffed at the neck, and the body firmly supported at the rump. If they are not held properly and securely, fractures or luxations of lumbar vertebrae can easily follow struggling. If a rabbit appears to be very stressed or excited, a sedative may be indicated to avoid injuries caused by handling. Midazolam at 0.5–1 mg/kg, IM, is often enough to adequately sedate the rabbit for a thorough physical examination.
Most techniques for physical examination suitable for dogs and cats may be applied to rabbits. A thorough oral examination, including palpation of the face and bottom of the jaw, should be performed to evaluate dental health. An otoscope or a pediatric nasal speculum can assist visualization of the molars. Conscious rabbits will usually resist a full dental examination, and sedation or anesthesia is required. Sex can be determined by depressing the external genitalia to reveal a slit-like vulva in females or the penis in males. The testicles descend at 10–12 wk. Normal body temperature is 103.3°–104°F (39.6°–40°C). Body temperature <100.4°F or >105°F is cause for concern.
Blood can be collected from the cephalic vein, lateral saphenous vein, and the jugular vein. The lateral saphenous vein is easy to access when the rabbit is held and resting on someone's forearm, with the restrainer holding the leg above the stifle joint. The lateral saphenous vein runs across the lateral aspect of the tibia at the middle of the length of the bone. In larger rabbits (>3 kg), the ear veins can also be used. The auricular or marginal ear vein provides a site for venous administration or catheterization. Drugs should not be injected through the ear veins, because this can lead to phlebitis and subsequent ear sloughing. Only physiologic crystalloid fluids should be administered via the ear vein. The central artery can be accessed for direct blood pressure monitoring during anesthesia; no drugs should be injected into the central artery. The auricular vasculature is sensitive to temperature; having the rabbit warm (or at least having the ear warm) and applying a topical anesthetic cream greatly facilitate these procedures.
Clinical pathology in rabbits varies from that in other domestic animals. The normal neutrophil:lymphocyte ratio is 1:1. The rabbit neutrophil is called a “pseudoeosinophil” or heterophil because of its red-staining cytoplasmic granules. Both the heterophil and the granules are smaller than the eosinophil and eosinophil red granules. Rabbits do not usually respond with a leukocytosis to an active infection. In case of stress, the ratio of the heterophils and lymphocytes changes toward a relative heterophilia without increasing the total WBC count. Many sick rabbits have hemoglobin and PCV values much lower than normal; this makes the PCV one of the best indicators of healthy or sick animals. Calcium metabolism in rabbits results in higher normal blood calcium levels (up to 16 mg/dL) and a wider range than in other animals, which can lead to an erroneous diagnosis of hypercalcemia. Rabbit urine ranges from yellow to brown or reddish. A dipstick can quickly differentiate normal rabbit urinary pigments from hematuria. Traces of glucose and protein are normal in rabbit urine.
Very few products are licensed for use in rabbits, leading to extra-label use of drug therapies approved for use in other species. Particular caution must be exercised in use of antibiotics that suppress normal GI microflora and result in enteric dysbiosis and/or enterotoxemia. This has been called “antibiotic toxicity.” Antibiotics contraindicated in rabbits include clindamycin, lincomycin, erythromycin, ampicillin, amoxicillin/clavulanic acid, and cephalosporins. The flea treatment fipronil is contraindicated in rabbits because of severe toxic reactions in some individuals. Supportive care for rabbits often includes aggressive IV fluid support. The maintenance fluid rate for rabbits (120 mL/kg/day) is much higher than that for dogs and cats. Hospitalized rabbits often require doubling of maintenance rates, or 10 mL/kg/hr. In addition to fluid support, pain control is also commonly needed. NSAIDs and opioids are often used in synergy. The dosage of meloxicam in rabbits is 1 mg/kg/day, which is also significantly higher than that in dogs and cats. Opioids such as oxymorphone or hydromorphine can readily be used and have not been shown to cause GI stasis. In most cases, additional force feeding is not required, and the rabbit should be offered food after fluid and pain management has been initiated. Syringe-assisted feeding can be offered to see whether the rabbit is interested in food intake. In rare cases in which the rabbit refuses to eat, eg, cases of severe hepatic lipidosis, active feeding is necessary; treatment may require aggressive nutritional support via syringe feeding, nasogastric tube (3–5 French), or pharyngostomy tube (soft esophagostomy tube designed for cats). The least invasive method is often the most successful approach. Various commercial products for assisted feeding of rabbits are available. Products are available for immediate critical care (eg, Emeraid®) as well as for longterm assisted feeding and to meet the needs of the recovering rabbit (eg, Recovery®, Recovery Plus®, Critical Care®).
Rabbit breeds of medium size are sexually mature at 4–4.5 mo, giant breeds at 6–9 mo, and small breeds (eg, the Polish Dwarf and Dutch) at 3.5–4 mo of age. The rabbit is an induced ovulator and, contrary to popular belief, has a cycle of mating receptivity; rabbits are receptive to mating ~14 of every 16 days. The degree of mating receptivity is indicated by the color of the vaginal orifice and by the amount of moisture on the labia. A doe is most receptive when the vagina is red and moist. Does that are not receptive have a whitish pink vaginal color with little or no moisture. Many breeders test mate the doe 10–16 days after breeding as a way to detect pregnancy, but this is unreliable. Palpation of the doe’s abdomen for “grape-sized” embryos in the uterus is a much better technique to detect pregnancy. The best time to palpate is 12 days after breeding. Pseudopregnancy is common in rabbits and can follow any induced ovulation, the introduction of a male rabbit in the environment, or other stimuli.
A ratio of 1 buck to 10 does is common practice, but many commercial growers find that 1 buck to 20–25 does is more economical. Bucks can be used daily without decreasing fertility; more frequent use requires periods of rest. The doe should always be taken to the buck’s cage for breeding. The breeding program should continue year round. Does that experience long periods of rest between litters tend to become obese and difficult to breed. Does constantly in gestation and lactation may become underweight, and their receptivity to the buck and fertility decrease dramatically. If breeding is delayed several weeks and the doe is given full feed, weight is quickly regained.
The gestation period is ~31–33 days. Does with a small litter (usually ≤4) seem to have a longer gestation period than does that produce larger litters. If a doe has not kindled by day 32 of gestation, oxytocin (1–2 IU) should be given to induce parturition; otherwise, a dead litter is almost always delivered sometime after day 34. Occasionally, pregnant does abort or resorb the fetuses because of nutritional deficiencies or disease.
Nest boxes should be added to the cages 28–29 days after breeding. If boxes are added too soon, the does foul the nests with urine and feces. A day or two before kindling, the doe pulls fur from her body and builds a nest in the nest box. The young are born naked, blind, and deaf. They begin to show hair on day 2–3 after birth, and their eyes and ears are open by day 10. Neonatal rabbits are unable to thermoregulate until about day 7. Rebreeding can occur any time after parturition, because the doe can conceive 24 hr after kindling. Some commercial growers use accelerated breeding schedules and rebreed 7–21 days after parturition, whereas most people raising rabbits for show or home use rebreed 35–42 days after parturition.
Most medium-sized female rabbits have 8–10 nipples, and many kindle 12–15 young. If a doe is unable to nurse all the kits effectively, kits may be fostered by removing them from the nest box during the first 3 days and giving them to a doe of approximately the same age with a smaller litter. If the fostered kits are mixed with the doe’s own kits and covered with hair of the doe, they are generally accepted. Moving the larger kits to the new litter instead of the smaller kits increases the chance of success. Does nurse only once or twice daily. Kits nurse <3 min. Kits are weaned at ~4–5 wk of age.
Kits can be hand-reared, but mortality is high. They should be kept warm, dry, and quiet. Kitten milk or goat milk replacer or a formula of ½ cup evaporated milk, ½ cup water, 1 egg yolk, and 1 tbsp corn syrup can be used. Feedings vary from ½ tsp to 2 tbsp, depending on the age of the kits. Kits should be fed only every 12 hr to avoid overfeeding and to mimic the natural feeding behavior of the doe. Cottontail kits start eating greens around day 15–18, whereas domestic rabbit kits are weaned when ~6 wk old.
Preoperative fasting is not required or recommended. Rabbits cannot vomit. Additionally, rabbit stomachs are never empty, even after prolonged fasting. However, a short fast (1–2 hr) should be done to assure that the oral cavity is free of food. Premedication with butorphanol or diazepam/midazolam will reduce stress from preoperative handling. Premedication with atropine will be useful for only a short time, because many rabbits have an atropinase that clears the drug from the system rapidly. Instead, glycopyrrolate may be used to reduce bradycardia and upper airway and salivary secretions (0.01–0.1 mg/kg, IM or SC, or 0.01 mg/kg, IV). Isoflurane is recommended for general anesthesia, but premedication with a combination of an NSAID and an opiate (such as meloxicam at 1 mg/kg, PO, and butorphanol at 0.4 mg/kg, IV) can reduce the minimum alveolar concentration (MAC) of isoflurane from 2.5% to 2.3%. Lidocaine administered as a constant-rate infusion has also been shown to reduce the MAC of isoflurane (lidocaine can be given at a loading dose of 2 mg/kg, IV, followed by 100 mcg/kg/min).
The long and narrow pharynx and large tongue make rabbits difficult to intubate. Laryngospasm can be minimized by application of lidocaine on the epiglottis. There are several reported techniques to intubate rabbits; all require selection of the appropriate tube size and length to avoid tracheal injury. A pediatric laryngeal mask, uncuffed Cole, or cuffed Murphy eye type endotracheal tube (ET) can be used, but selecting the appropriate size (2–4 mm) is critical. The risk of tracheal injury increases with repeated intubation attempts, but ET cuff pressure, prolonged duration of intubation, and movement of the ET during mechanical ventilation and animal positioning for anesthesia seem to be more critical because of the vascular anatomy of the rabbit trachea. Rabbits are best intubated with visualization, using an endoscope or similar technology. Direct visualization of the epiglottis and ET placement can also be accomplished by using a laryngoscope with a Miller 0 blade, a rabbit oral specula, and cheek dilators. The glottis should be visualized using the endoscope, and the tube carefully advanced toward the glottis. The natural position of the epiglottis is behind the soft palate. The ET can be used to disengage the glottis from the soft palate, and then introduced into the glottis and down the trachea. Care must be taken to not damage the arytenoid cartilages when inserting the tube into the trachea, because these cartilages reduce the diameter of the glottis significantly and can be easily damaged by a larger-size tube. If no visual aid is available, the rabbit can be intubated blindly, but this procedure requires much skill and has the potential for iatrogenic trauma if not performed properly. In the classic blind technique, the rabbit is placed in a sternal position with the head held and the nose pointing at the ceiling. The ET is guided behind the incisors and to the larynx. The operator listens for the sounds of inspiration and expiration and times the advancement of the ET with maximal inspiration. A second technique involves placing the rabbit in lateral recumbency with the head dorsiflexed. The ET is advanced along the hard palate to the back of the throat until condensation can be seen within the lumen of the ET. The condensation is used to judge the cycles of inspiration and expiration, and the ET is advanced at maximal inspiration. Proper ET placement should be confirmed regardless of placement method. An alternative to intubation is a supraglottic airway device (V-gel®). A species-specific pharyngeal device is placed in the oral cavity and advanced caudally until it sets in place automatically. The device sits on top of the glottis and seals the surrounding structures, creating an airtight connection between the trachea and the tube.
Adequate general anesthesia can be achieved for a short procedure with injectable ketamine (25–50 mg/kg) in combination with a tranquilizer such as xylazine (5–10 mg/kg, IM). The combination of ketamine (10–20 mg/kg, IM) and dexmedetomidine (0.125–0.25 mg/kg, IM) provides adequate anesthesia; ~⅓ of the original dose can be repeated if anesthesia needs to be prolonged. Atipamezole can be given IM in equal volume to dexmedetomidine volume for reversal.
It is critical for rabbits to start eating postoperatively, and analgesic treatment for 1–2 days will help prevent inappetence. A rabbit in pain may chatter or grind its teeth while sitting in a hunched position. Analgesic treatment may include opioid drugs such as buprenorphine (0.01–0.05 mg/kg, SC, IM, or IV, bid-tid) or butorphanol (0.05–0.4 mg/kg, SC or IM, bid-tid), or NSAIDs such as carprofen (1.5 mg/kg, PO or SC, bid), flunixin (0.5–2 mg/kg/day, PO, deep IM, or IV, for no more than 3 days), or meloxicam (1 mg/kg/day, PO or SC). Tramadol used at 11 mg/kg, PO, causes no adverse effects and has been reported empirically to be effective in rabbits. However, a study showed that this dose does not achieve plasma levels that would be considered adequate in people. Prolonged opiate exposure has not been associated with GI stasis.
Postoperative supportive care is critical to a successful surgical outcome. Hay and water should be offered as soon as possible after surgery. Alfalfa hay can be used to improve appetite. Banana is favored as a treat by many rabbits. Hand feeding or syringe-assisted feeding is necessary if the rabbit does not eat on its own soon after the surgery. If the rabbit does not eat within 2–3 hr after surgery, the analgesic protocol should be reevaluated. The rabbit should be assisted fed until it refuses further food intake in each session.
Castration can reduce aggressive behavior and is suggested for house rabbits and group-housed rabbits. It has no advantage for meat-type rabbits. The testicles are lateral and anterior to the penis, as in marsupials and not as in most other placental mammals. Castration is performed using a closed technique or by an open technique with closure of the large superficial inguinal ring to prevent herniation.
Female pet rabbits should be spayed because of the high risk of uterine cancer. Rabbits have two uterine horns connected to the vagina by two separate cervices. The oviduct loops around and is much longer than in cats or dogs. Ovariohysterectomy is more complicated in older or multiparous rabbits because of the large amount of fat in the mesometrium. Postoperative adhesions are a common complication, which may be reduced by calcium-blocker treatment (verapamil, 200 mcg/kg, SC, tid for 3 days). To avoid adhesions, all blood clots should be removed before closing the abdomen, and the GI tract should not be handled at all. The use of spay hooks is not recommended in rabbits, because the intestinal loops are easily damaged; tissue forceps (eg, Adson-Brown) are a better choice.
Although the vast majority of trichobezoars can be managed medically with aggressive fluid therapy (10–12 mL/kg/hr) and appropriate pain medication (eg, oxymorphone), a small percentage of GI cases need to be surgically corrected. Surgery should usually be considered if the condition has not improved after 24 hr of aggressive medical therapy. When gastrotomies are performed, the stomach is elevated by stay sutures through a cranial celiotomy incision. An incision is made through the greater curvature of the stomach. It is important to remove stomach contents from the pyloric sphincter and to examine the stomach lining for abnormalities. A fine, absorbable monofilament suture should be used for closure of the stomach wall and incorporate, but not penetrate, the gastric mucosa. Pre- and postsurgical care should include fluids and antibiotic therapy.
Rabbits can chew out skin sutures; therefore, skin closure should be performed with a 4-0 absorbable synthetic suture with a cuticular-cuticular pattern. Tissue glue may be added to finish this closure. Rabbits tolerate staples.
Rabbits may jump or scream when the traditional overdose of barbiturate is given in the marginal ear vein. Sedation with midazolam (5 mg/kg, IM or IV) or propofol (10 mg/kg, IV) is recommended before administration of the barbiturate. As a further precaution, euthanasia solution may be diluted 1:1 with saline to prevent a negative reaction and to reduce viscosity of the solution to facilitate a faster and smoother injection.
Toenails on the hindlimbs may severely scratch unprotected arms of handlers. Nails should be trimmed every 1–2 mo. Declawing is not recommended, but some rabbits tolerate application of adhesive nail caps.
Some breeders tattoo or place ear tags on their rabbits for identification purposes. For show purposes, the right ear is reserved for registration marks applied by registrars of the American Rabbit Breeders Association. A tag placed in the anterior cartilaginous part of the ear, nearer to the head, is less likely to be pulled out.