Found in the class Mammalia and order Rodentia, gerbils are classified in the suborder Myomorpha. This suborder was named for the deep and lateral masseter muscles attaching to the front of the muzzle and lack of premolar teeth. They belong to the superfamily Muroidea and subfamily Gerbillinae. Many exotic pets are not far removed from their wild counterparts and have undergone minimal selective breeding. In captivity, they are removed from their evolved environment and therefore less able to demonstrate their full range of behaviours, leading to implications for their health and wellbeing (Cousquer, 2008).
Anatomical specifics of gerbils
As mentioned above, gerbils are classified in the order Rodentia, typically characterised by a pair of continually growing incisors on the upper and lower jaw. These grow by several millimetres a week. They also have welldeveloped head muscles to enable them to crack open food and gnaw through materials such as wood or concrete (Morton, 2002). They are socially monogamous, group-living rodents, with a social organisation based on a stable reproductive pair (Razzoli and Valsecchi, 2010). Harderian gland secretions are particularly important, comprising lipids, proteins and protoporphyrin, and are carried by an excretory duct to the medial aspect of the nictitating membrane. These secretions are mixed with saliva and spread over the pelage during grooming (Batchelder et al, 2011).
The importance of environmental enrichment
With the growing popularity of exotic animals, it is important to understand and appreciate the normal behaviour and biology of various small mammal species to advise on their needs and suitability as pets (Flecknell, 2015). Appropriate housing and provision of necessary refinements are crucial, as housing can induce changes in brain and behaviour control mechanisms that evolved in a species’ natural environment. These mechanisms require specific environmental and social stimuli to function properly (Waiblinger and König, 2004).
How to implement this in the veterinary environment
Several factors can be addressed in the veterinary environment. While cage size is important, one study showed that a main factor in reducing stereotypic behaviours in these species was providing an artificial burrow made of two nest chambers and several tunnels. This suggests that the motivation to dig comes from the drive to have a burrow-like shelter (Habenicht et al, 2022). Other references support this, with Brown and Donnelley (2004) indicating that, for many rodents, the opportunity to retreat from light into a burrow is significant, with air temperature and relative humidity being of utmost importance. They indicate that air temperatures should be 18–26°C, with humidity between 30% and 70%. Any enrichment in the veterinary environment should ideally aim to reinforce the animals’ natural behaviours positively.
Gerbils are an active, yet docile, species. Some authors state that they are crepuscular or diurnal, while other studies indicate that they are nocturnal, showing higher activity during darker hours (Sorenson et al, 2005). It is also important to note that, when housed in a veterinary environment, although pairing would be beneficial to avoid pair-bond disruption, housing manipulations alone seem enough to induce behavioural changes in both male and female gerbils (Hendrie and Starkey, 1998). Additionally, when housed in a veterinary or domestic environment, gerbils should be provided with a sand bath to promote removal and reapplication of Harderian gland secretions through grooming, as well as natural outlets for chewing, burrowing and digging deep tunnels in sufficiently deep bedding (Flecknell, 2015).
Impacts of poor enrichment
It is important to implement environmental enrichment in the veterinary environment and monitor for stereotypic and repetitive behaviours, such as stereotypic digging (Flecknell, 2015). Conversely, one study noted that stereotypic behaviour was not triggered by small cage size, nor reduced by a four-fold increase in cage size or the introduction of an ethologically suitable substrate (Habenicht et al, 2022). Brown and Donnelley (2004) indicate that issues such as ringtail, nasal dermatitis and exacerbation of respiratory disease can develop if temperature and humidity are not controlled. Furthermore, if suitable provisions are not made, problems such as nasal dermatitis can develop through the build-up of secretions from the Harderian gland (Flecknell, 2015). Additionally, it is important to provide spatial complexity through vertical platforms, which provide opportunities for climbing, chewing and manipulation (Balcombe, 2006).
Conclusion
The sources and evidence presented clearly demonstrate that environmental enrichment is crucial for these species, as for any other, to keep the demands of stress within a tolerable range. Prolonged periods of high hypothalamic-pi-tuitary-adrenal activity in response to stress can have costly consequences, such as immunosuppression, disease, tissue atrophy and maladaptive behaviour (McPhee and Carlstead, 2010). Exotic animal practice presents many challenges, especially as many animals will mask signs of ill health for as long as possible; maintaining a stress-free environment and providing suitable enrichment is therefore very important (Ballard and Cheek, 2024). However, veterinary professionals must ensure that appropriate enrichments are provided for each species, as not all enrichments are useful or interesting for all species (Church, 2007).