Introduction

Although many herpetologists keep snakes for breeding, it is not uncommon for owners to retain a single animal of one species. Unlike some other taxonomic groups, female snakes may undergo reproductive activity and produce (infertile) eggs without necessarily contacting a male. Similarly, mating with a fertile male does not always ensure reproductive success. The cues for such activity are often environmental.

CASE PRESENTING SIGNS

A 5-year-old corn snake (Elaphe guttata) (Box 19.1), suspected to be female – although there was no previous history of reproductive activity – was presented with a month-long history of anorexia, reduced faecal production and condition loss.

BOX 19.1 Ecology of corn snakes

• Belong to Colubridae snake family, in the subfamily Colubrinae. Elaphe spp are rat snakes

• Range in the wild covers much of the USA and northern Mexico

• Normal habitat: overgrown fields, wooded groves and forest openings, rocky hillsides, meadowlands, common in disused farm buildings. Readily climb trees. Very secretive

• Usually attain 60 cm in length within the first year of life, and 1.2–1.8 m when fully grown

• Hibernate during the winter in colder regions. In more temperate areas, brumate (during cold periods they shelter in rock crevices and logs, and emerge to heat up in the sun on warm days)

• Free-ranging diet: lizards and tree frogs as young hatchlings, mainly small mammals (mice, rats, birds and bats) when adult. Kill by constriction

• Reproduction: sexual maturity at around 600 days of age. Breeding season March–May. Oviparous: lay 10–30 eggs per clutch, in rotting stumps or piles of decaying vegetation. Gestation of eggs is 60–65 days at around 28°C

• Popular pet, as relatively easy to keep in captivity. Often very colourful (many colour varieties) and frequently bred. Non-venomous. Live 15–20 years (up to 23 in captivity).

Husbandry

The snake was housed in a vivarium approximately 150 cm long × 60 cm wide × 60 cm high. The vivarium was constructed mostly of wood, with glass doors at the front and a partially meshed ceiling to provide ventilation. The substrate was bark chippings. Background heating was provided by a tubular heater near the top of the rear wall of the vivarium, connected to a thermostat. Although stimulation of reproductive activity was not intended, a period of cooling had occurred over the winter months during some renovations at the owner’s premises. A basking spot was present at one end of the vivarium, created by a ceramic bulb. The environmental temperatures were measured using a digital thermometer, and ranged from 27°C to 28°C during the day (dropping to 24°C overnight).

The day length was typically 12 hours although this had been reduced to 8 hours over the winter months; UV lighting was provided by a striplight (changed 4 months prior to presentation). A small hide box was present. The snake was generally handled daily for approximately 5 minutes, although handling had been reduced since signs of illness were noted.

A water bowl large enough for the snake to bathe in was provided, with the water changed daily. The animal was typically fed on two or three whole mice once a week, although, more recently, smaller mice had been offered to tempt the snake to eat.

Case History

Although it is not uncommon for snakes to be inappetent for short periods of time, the owner was concerned about the length of the current period of anorexia combined with weight loss. The owner had been administering fluids and nutritional support by gavage for 2 weeks prior to presentation. Although ecdysis was regular (every 6 weeks), the previous shed contained tears. Clinical signs reported included:

• Anorexia of approximately 2 month’s duration

• Condition loss, including a 4% loss in body weight (from 810 g to 776 g)

• Reduced amount of faeces passed (typically weekly, but now only once every 2–3 weeks).

Clinical Examination

Corn snakes are relatively easy to handle, and a complete clinical examination was possible. The findings were:

• Moderate body condition, weighing 776 g. Dorsal spinous processes of vertebrae readily palpated. Moderate muscle strength (no paresis noted)

• No stomatitis or other oral lesions that would result in discomfort and reduced appetite

• No signs of dyspnoea or respiratory secretions

• Some dysecdysis, with patchy/piecemeal shedding. (Snakes should shed their complete skin-including spectacles – in one piece.)

• No apparent dehydration. (It is difficult to clinically assess dehydration in snakes, but severe dehydration will result in a wrinkling of the skin and tacky mucous membranes.)

• Gender determined as female by probing (probe passed to a depth of only three scales caudal to the cloaca).

DIFFERENTIAL DIAGNOSES

As discussed in other cases, anorexia is a common presenting sign in reptiles, with many possible aetiologies. The main differentials considered for anorexia in this case were:

• Systemic disease, e.g. septicaemia.

• Gastrointestinal disease: infections (e.g. bacteria, protozoa (e.g. Cryptosporidium), nematodes), neoplasia, constipation (often associated with dehydration), inappropriate diet (e.g. feeding prey items that are too large)

• Metabolic disease, e.g. hypocalcaemia (often due to nutritional secondary hyperparathyroidism) resulting in paresis and delayed gastrointestinal motility

• Urogenital disease, e.g. renal failure

• Hepatic disease, e.g. hepatic lipidosis

• Normal reproductive behaviour: anorexia may be normal in gravid females, although this period is usually only for the final 15–20 days of gestation in corn snakes

• Reproductive disease: dysfunction may result in anorexia (often as a result of the space occupied in the coelomic cavity by the reproductive tract), e.g. follicular stasis or egg retention (due to dystocia or reproductive stasis)

• Respiratory tract disease: snakes with upper or lower respiratory tract infections are often anorexic, although clinical signs of respiratory difficulty are usually present (e.g. nasal discharge or open-mouth breathing)

• Behavioural causes of anorexia: intra- or inter-specific aggression when reptiles are housed together, psychological (e.g. associated with excessive noise or irregular light patterns)

• Neurological, e.g. loss of vision (e.g. due to spectacular abscesses) or smell (e.g. due to rhinitis)

• Other space-occupying lesions, e.g. neoplasia.

Case Work-Up

The history did not suggest obvious husbandry or dietary inadequacies that may have predisposed to disease. Apart from the obvious loss of body condition, the physical examination did not reveal any significant findings.

Haematology and biochemistry

A blood sample was taken by cardiocentesis to perform a general health profile, investigating for signs of generalized infection or inflammation as well as renal or hepatic disease (Table 19.1). Although a few parameters were outside the normal ranges reported for corn snakes, none were significantly abnormal. A relative heteropenia was present, but the total white cell count was within normal limits and white cell morphology was normal on microscopy. Often poikilocytosis is noted with anorexia, but was not present in this case. Elevations in calcium and phosphorus are sometimes associated with reproductive activity.

Table 19.1 Corn snake blood results (with reference ranges for comparison)