Introduction

Macropods are a unique group of marsupials found in Australia and surrounding islands. Knowing their unique anatomy and physiology differences when compared to eutherian mammals can help the clinician differentiate normal peculiarities from abnormal pathologies. The purpose of this presentation is to provide a clinician with a general overview of macropod medicine, including common procedures and the most frequently encountered medical conditions of captive macropods in North America. More detailed references on macropod medicine and pathology are available:^4,8

Taxonomy

Class Mammalia: Subclass Theria: Infraclass Metatheria: Order Diprotodontia: Family Macropodidae

Species that are more likely to be encountered in private practice in North America include the following:

 Bennett's Wallaby (Macropus rufogriseus); aka Red-necked Wallaby, King Island Wallaby

 Red Kangaroo (Macropus rufus)

 Eastern Grey Kangaroo (Macropus giganteus)

 Western Grey Kangaroo (Macropus fuliginosus)

 Tammar Wallaby (Macropus eugenii)

 Wallaroo (Macropus robustus)

Unique Anatomy

Macropods are often grouped into one of three classifications based on their feeding strategies: browsers, grazers, and intermediate. Browsers eat primarily leaves, tend to be smaller, have large first maxillary incisors that help with finer prehension of food, have a relatively flat dental arcade with all molars reaching occlusion at the same time, and lack molar progression. Grazers eat primarily grass, tend to be larger, have three pairs of similarly sized maxillary incisors used to crop grass, have a dental arcade that is more curved with only about two molars in each arcade in occlusion at any given time, and exhibit molar progression. Molar progression is an adaptation where older, worn molars move rostrally and are shed as they go out of occlusion as they are replaced with newer, unworn caudal molars. The intermediate grade consists of species that eat a varied diet and share dental characteristics of both groups.

Macropods possess three main groups of salivary glands. The parotid glands produce saliva containing higher levels of phosphates and bicarbonate that buffer the contents of the forestomach. The mandibular salivary glands produce a hypotonic solution of sodium chloride and potassium chloride that is used to lick the forearms as a cooling mechanism. The sublingual salivary glands are the smallest and lack specialized differentiation.

The female macropod's pouch is well developed and contains four nipples, which can each develop independently of one another. Epipubic bones extend from the pelvis to help support the pouch. The macropod foot is large, with digit IV being the largest. Macropods lack an ossified patella. The corpus callosum is absent. The spleen has a triangular or triradiate shape. Macropods possess cervical thymi in addition to thoracic thymi.

Reproduction

A detailed reference to macropod reproductive physiology is available.⁷ The female's reproductive tract consists of two ovaries, two oviducts, two uteri, two lateral vaginas, one median vagina, and the opening into a cloaca. Ovariohysterectomies must be performed with caution to avoid transection of the ureters which run through the loops formed by the lateral vaginas. Some species have a permanently patent median vagina, while in others, the pseudovaginal canal is reformed at each parturition. Males possess a pendulous scrotum that is cranial to the penis, which protrudes from the cloaca. Males possess bulbourethral glands and a relatively large prostate. Castration is routine, with scrotal ablation frequently performed.

The placenta is diffuse, epitheliochorial, and choriovitelline. Joeys are born relatively undeveloped, but use strong forearms to climb their way to a pouch. There they form a semi-permanent attachment to a nipple and continue their development. Macropod milk changes content as the joey ages, and a female can simultaneously produce different types of milk from different nipples. Many macropods can exhibit embryonic diapause where a second ova is fertilized during a post-partum estrus, but the blastocyst remains in arrested development until lactation for the first joey ceases.

Nutrition

A detailed reference of macropod nutrition is available.² Macropods have a metabolism that is approximately 30% lower than similar-sized eutherian mammals. Basal Metabolic Rate (BMR) ranges from 57–88% of a eutherian mammal's BMR. BMR for macropods is calculated using the formula: BMR = 70.5 x body weight (kg)^0.49. Macropods have a relatively lower body temperature that ranges from 91–97°F (33–36°C).

Macropods are herbivorous foregut fermenters. The stomach consists of a sacciform forestomach, tubiform forestomach, hindstomach, and pylorus. Merycism is a regurgitation and reingestion (but no remastication) of forestomach contents that should not be confused with choke or other pathologies. A cecum is present, but is not a major site of fermentation. Firm round fecal pellets are formed in the distal colon.

Unlike eutherians, macropods possess a slower mechanism for digestion of lactose, which works well for their low lactose milk. Cow/goat milk or standard commercial milk replacers should not be used for hand-rearing due to lactose levels that can result in osmotic diarrhea, gastrointestinal bacterial overgrowth, or cataracts. Hand-rearing can be challenging, requiring specialized milk, specialized nipples, and a great deal of care and expertise. Consultation with specialized resources or experts is highly recommended before attempting hand-rearing.⁶

Captive macropod diets should consist of a good quality grass hay or grass pasture ad lib. A commercial macropod pelleted ration can be offered in moderation. Vegetables can be given in small amounts, but fruit, bread, or other easily fermentable items should only be an occasional treat. Macropods should have access to fresh clean water and a salt block. Vitamin E supplementation may be needed to help prevent myopathies.

Captive Management

Macropods should be kept in enclosures that provide shade and shelter and minimize the chance of trauma caused by running into barriers. Sharp corners and dead ends should be avoided. The species' natural history should be reviewed to ensure that individuals are being housed in appropriate social groupings and sex ratios. Macropods are especially susceptible to stress caused by improper management, resulting in many diseases associated with immunosuppression. A text on captive management is available.³

Restraint and Anesthesia

Young or tractable individuals of the smaller species may be handled with manual restraint or by placement in a cloth "pouch". This should be limited to very short procedures or to administer drugs. Operant conditioning can also be used to allow some minor procedures. Otherwise, handling of macropods requires sedation or anesthesia, which many need to be delivered by dart. Benzodiazepines, such as midazolam IM or IV or diazepam IV, work well for minor sedation. Anesthesia can be achieved with Telazol or a ketamine/dexmedetomidine combination. Midazolam can be added for additional sedation and butorphanol can be added for analgesia. The author uses the following drug dosages for adult healthy individuals for routine exams:

Eastern Grey Kangaroo:

 Sedation: diazepam 1 mg/kg IV or midazolam 0.2 mg/kg IV or 0.3 mg/kg IM.

 Immobilization: induce with ketamine 3 mg/kg IM, dexmedetomidine 0.025 mg/kg IM, and midazolam 0.02 mg/kg IM; maintain on isoflurane; reverse with atipamezole 0.25 mg/kg IM.

Bennett's Wallaby:

 Sedation: diazepam 1 mg/kg IV or midazolam 0.2 mg/kg IV or 0.3 mg/kg IM.

 Immobilization: induce with ketamine 4 mg/kg IM, dexmedetomidine 0.025 mg/kg IM, and midazolam 0.1 mg/kg IM; maintain on isoflurane; reverse with atipamezole 0.25 mg/kg IM.

Intubation of some species of macropods can be challenging due to a small oral cavity and poor visualization of the glottis. Specialized laryngoscopes, use of an endoscope, and blind techniques can be employed to assist with intubation.

Macropods are susceptible to capture myopathy caused by excessive struggling or exertion during immobilizations. Prevention with proper diet/supplementation, minimization of stress, and rapid induction are preferable to treatment, which can be challenging. Treatment is aimed at maintaining hydration and renal perfusion, providing sedation and muscle relaxation, correcting acid/base and electrolyte imbalances, and reducing stress.

Basic Medical Procedures

Blood is most easily collected from the lateral tail vein at the base of the tail at the 3 and 9 o'clock positions. The jugular, cephalic, saphenous, and femoral veins can also be used. Intravenous catheters are also easily placed and maintained in the lateral tail vein. A detailed hematology reference is available.

A thorough physical exam is the key to a preventative medicine program for macropods. Weights and body condition scoring should be recorded. Fecal exams and fecal cultures can detect enteric pathogens. A CBC and chemistry panel can detect underlying disease. Macropods don't usually develop a dramatic leukocytosis even to severe inflammatory disease. Mild leukocyte changes and hyperglobulinemia may indicate underlying inflammation. Vaccines commonly used in macropods include killed rabies and tetanus toxoid. Toxoplasmosis and macropod retrovirus can be screened with serology.

Bacterial Diseases

Mycobacteriosis

Mycobacteriosis in macropods is most often associated with immunosuppression and often caused by species within the M. avium complex (MAC). The chronic, slowly progressive disease often manifests as skin lesions, osteomyelitis, and lymphadenitis. Treatment for this potentially zoonotic disease is usually unrewarding. y

Alveolar Osteomyelitis ("Lumpy Jaw", Oral Necrobacillosis)

Alveolar osteomyelitis is infection of the tooth roots and surrounding bone and soft tissues. The disease can be caused by any opportunistic bacteria, but anaerobes are frequently involved. Oral trauma and improper diets that interfere with proper dental wear and molar progression predispose an individual to this disease. Immunosuppression caused by stress and improper husbandry and sanitation can dramatically increase the frequency of this disease. Treatment should consist of aggressive dental extraction and surgical debridement, systemic and possibly local antibiotic treatment, and supportive care.

Pouch Infections

Infections of the pouch usually present as a pouch that is excessively moist, greasy, or foul-smelling. This is an important rule-out for cases of pouch prolapse, which can be a normal occurrence in some species around puberty and during estrus. Treatment consists of topical cleansing and antimicrobials.

Tetanus

Macropods are susceptible to tetanus caused by Clostridium tetani, with clinical signs similar to those in other species (muscular rigidity, clonic spasms, etc.). Treatment is usually unsuccessful with clinical signs progressing to death within 48 hours. Prevention is easily achieved with tetanus toxoid vaccination.

Fungal Diseases

Dermatophytosis

This potentially zoonotic disease causes skin lesions similar to those in other species (i.e., pruritic, sometimes circular, areas of alopecia). Trichophyton mentagrophytes or sometimes Microsporum gypseum can often be cultured on DTM to achieve a diagnosis. The disease can be self-limiting, but severe cases may require topical and/or systemic antifungal drugs.

Candidiasis

Infection of the oral cavity and/or gastrointestinal tract with Candida albicans can result in oral plaques and yellow, foul-smelling diarrhea. Yeast can be observed on cytology to confirm a diagnosis. Treatment is achieved with nystatin or systemic antifungals. The disease is often associated with immunosuppression or suboptimal hygiene, and is most often seen in joeys, particularly hand-reared ones.

Viral Diseases

Herpesviruses

Three herpesviruses have been described in macropods. MaHV-1 and MaHV-2 are alpha herpesviruses associated with systemic fatal disease in macropods in Australia. MaHV-3 has been described in both North America and Australia and may be associated with an ulcerative cloacitis.

Wallaby Retrovirus

Wallaby retrovirus is a poorly understood disease that may be associated with an immunosuppressive syndrome. Serology is available from Purdue ADDL.

Parasitic Diseases

Toxoplasmosis

Toxoplasmosis is a significant disease of macropods, causing neurologic, hepatic, respiratory, or systemic clinical signs or acute death. Prevention is aimed at reducing exposure to felid feces. Diagnosis can be made with paired serology, PCR, or histopathology. Atovaquone has shown some success in treatment, but treatment is often challenging. Supportive care should also be given. Although the disease is zoonotic, people can only contract it from macropods by eating their undercooked meat. A review of this disease has been recently published.⁵

Coccidiosis

Coccidia (Eimeria spp.; occasionally Isospora spp.) are usually associated with joeys, especially hand-reared ones. Stress and overcrowding can contribute to the persistence of the disease, which may become fatal for some individuals. Toltrazuril has had better efficacy than traditional coccidiostats. Prophylactic treatment (e.g., monthly amprolium) is performed by some.

Helminths

Many helminth species have been described in wild macropods. Many are commensals, and the pathogenicity of most species is relatively unknown. If clinical signs are present or worm burdens are high, treatment with traditional dewormers should be performed.

Other Diseases

Trauma

Head and spinal trauma are common following acute stressors that cause macropods to startle and run into barriers or other objects in their enclosure. Enclosure design and other preventative measures are important. Treatment is similar to that for domestic species.

Neoplasia

A variety of neoplastic diseases have been described in macropods. Mammary carcinomas and oral squamous cell carcinomas appear to have increased incidences in this taxa, both with poor prognosis.

References

1.  Clark P, ed. Haematology of Australian Mammals. CSIRO Publishing, Collingwood, Victoria, Australia. 2004.

2.  Hume ID, ed. Marsupial Nutrition. Cambridge University Press, New York, New York. 1999.

3.  Jackson S. Macropods. In: Jackson S, ed. Australian Mammals: Biology and Captive Management. CSIRO Publishing, Collingwood, Victoria, Australia. 2003:245–296.

4.  Ladds P, ed. Pathology of Australian Native Wildlife. CSIRO Publishing, Collingwood, Victoria, Australia. 2009.

5.  Portas TJ. Toxoplasmosis in macropodids: A review. J Zoo Wildlife Med. 2010;41:1–6.

6.  Staker L, ed. The Complete Guide to the Care of Macropods. Matilda's Publishing. 2006.

7.  Tyndale-Biscoe H, Renfree M, eds. Reproductive Physiology of Marsupials. Cambridge University Press, New York, New York. 1987.

8.  Vogelnest L, Portas T. Macropods. In: Vogelnest L, Woods R, eds. Medicine of Australian Mammals. CSIRO Publishing, Collingwood, Victoria, Australia. 2008:133–225.