Anorexia in Reptiles
Anorexia is probably one of the most common issues faced by reptile owners. The reason for an anorexic period may be due to normal physiological changes (e.g. just before shedding, egg laying or hibernation, brumation, etc.). or related to improper management, such as poor nutrition, inappropriate temperature, humidity and/or substrate, stress caused by cage mates or owner, or due to both infectious and non-infectious diseases. Owners should assess the living conditions of their animal to determine if the cause may be due to poor management, if no fault in husbandry is found the cause may be down to physiological changes or disease, if in doubt take the animal to a vet. As a general rule, a reptile going through a normal physiological phase of anorexia should not lose more than 10 percent of their body weight. To monitor this accurately, it is good husbandry practice to weigh the individual animal on a routine basis (e.g. once a month).
Reasons for Refusal to Eat
Poor environmental conditions such as incorrect heating, lighting, humidity and substrate can all be contributors to the development of anorexia. Environmental temperature can effect nutritional uptake because reptiles and amphibians are ectothermic, that is to say they rely on their surroundings to maintain their body temperature. There is an optimum preferred temperature zone (OPTZ) that will allow their enzymes and metabolic pathways to function at their optimum levels, so environmental temperature will influence the rate of digestion of the food offered. If reptiles are kept at temperatures lower than their OPTZ than digestion may not occur before the prey item becomes rancid inside the animal. Similarly if kept at too high temperatures the reptile may not be stimulated to eat at all and dehydration and heat stress may set in. Incorrect humidity may cause the onset of skin or respiratory disorders which would also result in diminished appetite. Lighting is important for providing day/ night cycles so the animal may know whether it's daytime or night-time and what season it is by the day length. Many reptiles rely on light cycles to determine when to breed, hibernate and perform other seasonally determined physiological processes. Anorexia may result from stress from an inability to determine the correct season or time of day and therefore are unable to respond appropriately. Incorrect UV lighting would further induce a deficiency of vitamin D causing the animal to become anorectic through illness. Ingestion of substrate may also be a cause of anorexia if large quantities of substrate were consumed, either intentionally or accidentally, causing impaction and risk of internal rupturing.
Inappropriate Food Item/Feeding Method
The type of feed given and method in which it's presented may be a cause for refusal, for instance, wild caught snakes have been known to refuse white lab rats but would strike at brown rats. Some animals such as snakes may see one type of animal as a food source, for example some snakes which are raised on mice will refuse to eat rats, and snakes which are fed live prey may refuse frozen thawed. In such cases introducing different food items to a non feeding animal may be a solution. It is a good idea to enquire about the animals feeding history before purchasing. Food items must be appropriate to the species it's being fed to, food which is too big may not be accepted by the animal. Some lizards have been known to 'go off' a certain food item if given a varied diet and may simply have a preference over what it's being fed. For example, in the past my geckos have refused crickets but readily ate locusts and mealworms.
It is best to feed animals during their most active periods, nocturnal species such as leopard geckos or corn snakes naturally hunt during the night or twilight hours so may accept food more readily at these times. Some species are shy feeders and prefer to eat alone, hidden away from sight.
Live food should be removed if not eaten, crickets left in with lizards have been known to cause skin damage by insect bites. Pre-killed vertebrate prey is strongly recommended to prevent potential suffering of both prey and predator species.
Stress and Social Competition
Stress may be caused by limited space and lack of hides which lead to "maladaptive syndrome”. That is to say an animal which has adapted poorly to the environment it's been given. If not provided with sufficient hides, the animal may feel over-exposed so will become stressed and refuse food. Another cause of stress may be over-handling of shy species (e.g. Royal Python and Chameleon) or overcrowding causing stress through bullying and competition.
New animals are usually very stressed after a move and may need time to adapt to their new surroundings first before they are ready to eat. There should be some concern if the new pet has not eaten in the first week and a change in management may be required, perhaps the animal feels too exposed or is being disturbed too much. Wild caught animals often refuse to eat as they endure a great deal of stress during capture and captivity. Some species, such as the royal python are predisposed to short periods of anorexia but Captive Bred royals do not have the same feeding issues to the same extent as wild caught individuals.
Illness or Physiological Changes
Anorexia may be a sign that your animal is suffering from some form of disease or disorder. It may also be caused in response to normal physiological changes such as shedding, preparing to hibernate or in preparation of the breeding season. During the shedding process many animals will refuse to eat during this time. Females may also refuse if they are ovulating, even if they have not been bred they are still capable of producing eggs. A suitable place to lay must be provided, even for unbred females to prevent egg binding (when the eggs become stuck inside the animal). Post Hibernation Anorexia (PHA) as observed in chelonians can be an issue in those not prepared appropriately before hibernation or not properly cared for after waking from hibernation.
PHA is a condition seen in mediterranean species of tortoise which hibernate during winter months. Those affected by PHA often display signs of systemic or respiratory tract infections (such as runny nose syndrome) and low body weight in relation to length (Jacksons ratio). Dehydration is also apparent in such cases, treatment requires aggressive fluid therapy and nutritional support by a vet. Causes may be due to disease during or before hibernation, poor nutrition leading to poor fat reserves before hibernation, owners failure to observe recovery from hibernation for several days so no food has been offered at the critical time or exposure to cold whether immediately after recovery. To prevent PHA it is important to attend to the disease before hibernation and those too ill or underweight should not be hibernated at all. Tortoises should be checked regularly throughout hibernation, at least once or twice a week so if the tortoise does come out of hibernation early, food and water may be provided immediately. Bathing the tortoise immediately after waking in warm water and cleaning the nose, eyes and mouth can help stimulate appetite. Tortoises which have recovered from hibernation, even if they have awoken early should not be re-hibernated the same winter.
If anorexia in a reptile has persisted for some time it is essential that the animal is rehydrated before attempting to feed. Initial feeding after this should be started off at very low levels. This is because excess calories and proteins cause rapid uptake of glucose from the bloodstream into the cells, which takes potassium and phosphorus with it. This can lead to life threatening hypokalaemia and hypophataemia.