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InFocus

Small mammal reproductive disease

Reproductive disease in small exotic mammals is a fairly common occurrence and can be quite alarming to the client, especially when haemorrhage occurs

Reproductive presentations are fairly common in exotic small mammal species. Clinical signs can vary but often reproductive disease presents with some degree of lethargy, anorexia, swelling of the affected area and, in females, vaginal discharge can be seen with a range of ovarian and uterine conditions. Abdominal ultrasonography can be very useful in cases of reproductive disease; however, smaller patients often need to be sedated to allow a diagnostic scan. Abdominal radiography can also be useful, although can be less sensitive than ultrasound. Some commonly encountered reproductive diseases in our small exotic mammals are discussed in brief below.

Dystocia

Dystocia is encountered in all small mammal species; however, it is less commonly seen in rodent species with large litter sizes such as rats and mice (Martorell, 2017). More commonly affected species include guinea pigs and chinchillas, as they tend to have smaller litter sizes and larger foetal sizes (Bennett, 2012). Older guinea pigs can be at a higher risk of dystocia if not bred before six months of age as a cartilaginous fusion of the pelvic symphysis occurs up until six to nine months of age and, if parturition has not occurred by this time, this matures to a bony fusion (Peters, 1991). This bony fusion makes it difficult for the pelvis to expand to pass foetuses and results in an obstructive dystocia. Chinchillas have an average of two young per litter (Keeble, 2009) and so if only one foetus is present then this can grow to a larger size and cause obstructive dystocia during parturition (Figure 1). Other causes of dystocia in small mammals can include uterine inertia, uterine torsion or malpositioned foetuses (Hoefer and Crossley, 2002).

FIGURE (1A) Due to their small litter sizes, chinchillas are predisposed to dystocia if only one foetus survives, such as in this case which required surgical caesarean
FIGURE (1B) The same chinchilla kit was successfully delivered via caesarean. Chinchilla kits are precocious and so are often born larger than kits of other species

Dystocia should be treated in a similar way to our canine and feline patients; however, the majority of cases are obstructive in nature and so calcium gluconate and oxytocin should not be administered until obstructive dystocia has been ruled out. Radiographs and ultrasonography are useful tools in diagnosis and potential surgical planning (Kondert and Mayer, 2017). Surgical caesarean is usually indicated in small mammals and is recommended in cases of dystocia lasting greater than four hours (Hoefer and Latney, 2009).

Pregnancy toxaemia

FIGURE (2) Pregnancy toxaemia can cause severe, acute illness in guinea pigs. This guinea pig successfully began to eat again after intensive hospitalisation following post-partum pregnancy toxaemia

Pregnancy toxaemia occurs in guinea pigs from approximately two weeks prior to parturition up to two weeks post-partum (Hawkins and Bishop, 2012; Figure 2). It occurs when the energy requirements of the sow are higher than the energy intake, due to the demands of pregnancy and lactation, resulting in a negative energy balance. As a result, the body catabolises fat stores which results in a metabolic acidosis and ketosis (Hoefer and Latney, 2009). Clinical signs are acute in onset and include purulent or haemorrhagic vaginal discharge, abdominal distension, lethargy, anorexia, pyrexia and death (Hawkins and Bishop, 2012). Urinalysis will show ketonuria and proteinuria with bloodwork showing hypoglycaemia, hyperlipidaemia, hyperkalaemia and metabolic acidosis (Hoefer and Latney, 2009). This is a medical emergency and fluids with dextrose should be administered via intravenous or intraosseous routes, along with administration of calcium gluconate, oral glucose and magnesium sulphate (Hoefer and Latney, 2009). Nutrition via syringe feeding or a nasogastric tube should be instigated and maintained until the patient has fully recovered; however, prognosis is grave. Prevention is important and involves reducing stress in pregnant and post-partum sows, not breeding obese sows and avoiding changes in the diet or environment (Hawkins and Bishop, 2012).

Cystic ovaries

Cystic ovaries are commonly encountered in guinea pigs and is reported to be the most common disease of the guinea pig reproductive tract (Minarikova et al., 2015). Numerous studies exist, citing the incidence from 58 to 100 percent in sows of three months to five years old (Kondert and Mayer, 2017). Clinical signs include bilateral, non-pruritic flank alopecia, aggression, weight loss and anorexia, with occasional haematuria or haemorrhagic vaginal discharge (Bennett, 2012). Diagnosis can be made with palpation, abdominal ultrasound and abdominal radiography (Hoefer and Latney, 2009). Ultrasound-guided fine needle aspiration of the cysts can relieve symptoms temporarily; however, these inevitably refill within a few days to weeks (Kondert and Mayer, 2017). Medical management can involve the injection of leuprolide acetate, gonadotrophin-releasing hormone or human chorionic gonadotrophin at varying intervals (Hoefer and Latney, 2009); however, inevitably the cysts reoccur and surgical ovariohysterectomy is now the recommended treatment for long-term cure (Bennett, 2012).

Pyometra

FIGURE (3) Pyometra can occur in any entire female exotic mammal. In the case of this African pygmy hedgehog the purulent material was inspissated and so would not have been cleared with medical therapy alone

Pyometra (Figure 3) has been observed in a range of small mammal species such as hamsters, guinea pigs, chinchillas and rats; however, it is quite a rare presentation. Clinical signs can include acute onset anorexia and lethargy, mucoid to mucopurulent or haemorrhagic vulval discharge and anogenital fur staining (Donnelly, 2012), with some guinea pig owners reporting polyuria and polydipsia (Bennett, 2012). Diagnosis is often by ultrasonography (Hawkins and Bishop, 2012) with additional testing considered, including abdominal radiography, vaginal cytology, haematology and biochemistry (Kondert and Mayer, 2017). Ovariohysterectomy is the treatment of choice for non-breeding females; however, in those that are destined for future breeding, treatment with algepristone can be considered (Kondert and Mayer, 2017) in conjunction with appropriate analgesia, antibiosis and supportive care such as fluid therapy and syringe feeding as required.

Neoplasia

Reproductive neoplasia is fairly common in small mammals and rodents (Figures 4 and 5). Uterine adenocarcinoma is the most common neoplasia of female rabbits with a study of 849 female rabbits showing 75 percent had uterine neoplasia by the age of seven years (Harcourt-Brown, 2017). Ovarian neoplasias have been reported in rats with adenomas seen most commonly (Gregson et al., 1984). Ovarian tumours have also been reported in mice, hamsters and gerbils (Martorell, 2017). Ovarian adenocarcinomas, uterine leiomyomas and leiomyosarcomas have been reported in guinea pigs (Bishop, 2002). Clinical signs include anorexia, lethargy, abdominal pain and distension and in some instances vaginal discharge. Abdominal ultrasound or radiography aid in diagnosis and the treatment of choice is surgical ovariohysterectomy.

FIGURE (4) Uterine neoplasia is common in older female rabbits and can result in a gross distension and obvious pathology of the uterus
FIGURE (5) A mammary mass on the right flank of a rat. Benign fibroadenomas account for 80 to 95 percent of all mammary masses in rats

Mammary neoplasia is closely linked with reproductive disorders and in rats increased oestrogen administration increases the incidence of mammary adenocarcinomas (Orr, 2002). In rats, benign fibroadenomas make up the majority (80 to 95 percent) of mammary neoplasias seen in males and females (Hoefer and Latney, 2009); however, in mice 90 percent of mammary tumours are malignant adenocarcinomas or fibrosarcomas (Sayers and Smith, 2010). Ovariectomised rats are reported to have a lower incidence of mammary and pituitary tumours (Hotchkiss, 1995). Approximately 50 percent of mammary neoplasias in guinea pigs are malignant, but often slow to metastasise (Hawkins and Bishop, 2012). Quality of life is often compromised when these tumours grow quite large and impede the patient’s ability to ambulate normally. These tumours can grow anywhere along the flanks and ventrum as mammary tissue extends from the shoulders and axillae to the inguinal area (Martorell, 2017). Fine needle aspiration of these masses, usually under sedation or general anaesthesia, will provide diagnosis and prognosis, with surgical excision being the treatment of choice. Neutering during the same general anaesthesia can also be considered to prevent the reoccurrence of these tumours (Martorell, 2017).

In summary

Reproductive disease in small exotic mammals is a fairly common occurrence, and can be quite alarming to the client, especially when haemorrhage occurs. Ultrasonography and radiography can be very useful diagnostic tools. Often surgery with or without ovariohysterectomy or orchiectomy is the treatment of choice. In these cases, adequate pre-, peri- and post-operative care should involve supportive nutrition, adequate analgesia and antibiotic coverage as necessary.

References

Bennett, R.A.

2012

Soft Tissue Surgery. In Quesenberry, K.E. and Carpenter, J.W. (eds.) Ferrets, Rabbits and Rodents: Clinical Medicine and Surgery. 3rd ed. Missouri: Elsevier Saunders, pp. 326-338

Bishop, C.

2002

Reproductive medicine of rabbits and rodents. Veterinary Clinics of North America: Exotic Animal Practice, 5, 507-535

Donnelly, T.M.

2012

Disease Problems of Chinchillas. In Quesenberry, K.E. and Carpenter, J.W. (eds.) Ferrets, Rabbits and Rodents: Clinical Medicine and Surgery. 3rd ed. Missouri: Elsevier Saunders, pp. 311-325

Gregson, R., Lewis, D. and Abbott, D.

1984

Spontaneous ovarian neoplasms of the laboratory rat. Veterinary Pathology, 21, 292-299

Harcourt-Brown, F.

2017

Disorders of the Reproductive Tract of Rabbits. Veterinary Clinics of North America: Exotic Animal Practice, 20, 555-587

Hawkins, M.G. and Bishop, C.R.

2012

Disease Problems of Guinea Pigs. In Quesenberry, K.E. and Carpenter, J.W. (eds.) Ferrets, Rabbits and Rodents: Clinical Medicine and Surgery. 3rd ed. Missouri: Elsevier Saunders, pp. 295-310

Hoefer, H.L. and Crossley, D.A.

2002

Chinchillas. In Meredith, A. and Redrobe, S. (eds.) BSAVA Manual of Exotic Pets. 4th ed. Gloucester: British Small Animal Veterinary Association, pp. 65-75

Hoefer, H. and Latney, L.

2009

Rodents: urogenital and reproductive system disorders. In Keeble, E. and Meredith, A. (eds.) BSAVA Manual of Rodents and Ferrets. Gloucester: British Small Animal Veterinary Association, pp. 150-160

Hotchkiss, C.E.

1995

Effect of surgical removal of subcutaneous tumours on survival of rats. Journal of the American Veterinary Medicine Association, 206, pp. 1575-1579

Ashton Hollwarth

Ashton Hollwarth, BSc, BVMS, CertAVP (Zoo Med), MRCVS, studied in Western Australia and moved to England following graduation. She is currently enrolled in an ECZM residency in Avian Medicine and Surgery at Great Western Exotics. Ashton gained her Certificate of Advanced Veterinary Practice in Zoological Medicine in 2020 and became an Advanced Practitioner in Zoological Medicine in 2021.


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