The older turtle or tortoise: the diet that changes with age, and why eating less is not just age

Quick answer

The diet that grew a healthy juvenile will make an adult ill. In several species the shift is from mostly animal protein to mostly plants.

Chelonians live a long time, and most animals owners describe as elderly are in fact adults in their prime. That matters, because "it is just getting old" is one of the least likely explanations for a turtle or tortoise that has gone off its food.

Two things are usually going on. The diet has not changed as the animal matured, and something in the enclosure has drifted, most often temperature or an ultraviolet lamp that has quietly stopped working while still producing light.

• Many aquatic turtles are largely carnivorous as juveniles and become largely herbivorous as adults. The feeding plan has to change with them.
• Check temperature and ultraviolet output before you consider illness. A cold chelonian cannot digest and will not eat.
• An ultraviolet lamp stops emitting useful output long before it stops emitting visible light.
• Weight is the measurement. Weigh on the same scale, at the same point in the routine, and keep the record.
• Never allow an underweight, unwell or undiagnosed animal to brumate.

Decide in 60 seconds

The diet shift owners miss

Aquatic and semi-aquatic turtles.
Red-eared sliders and many related species begin life as opportunistic carnivores, taking insects, larvae and small aquatic animals, and they become substantially more plant-eating as they mature. In the wild, an adult slider takes a great deal of aquatic vegetation.

In captivity the diet often does not follow. The animal continues on the same protein-rich pellet and the same portions of animal food that suited a fast-growing juvenile, and the consequences accumulate: excessive growth rate, shell pyramiding and deformity, obesity that prevents full retraction into the shell, fatty liver, and kidney disease.

Correcting it means shifting the balance towards plants as the animal matures: dark leafy greens, safe aquatic plants, and a reduced pellet portion, with animal protein becoming a smaller component. It also usually means feeding less often. A growing juvenile eats daily; an adult does not need to.

Herbivorous tortoises.
Mediterranean species such as Hermann's and Russian tortoises, and grazing species such as sulcata and leopard tortoises, need a high-fibre, low-protein, low-sugar diet with a favourable calcium balance. For the grazing species in particular, grasses and hay should be the bulk of the intake rather than a garnish.

The classic failures are supermarket lettuce, which is mostly water with little nutritional value, large amounts of fruit, which is not part of the diet of a Mediterranean or grassland tortoise, and protein sources such as dog food, cat food, bread and dairy, which have no place at all. These produce fast growth, a lumpy pyramided shell, bladder stones and renal disease.

Omnivorous species.
Box turtles and some others genuinely remain omnivorous, and their proportions change less dramatically. Even here, portions and frequency should reduce as growth finishes.

The general principle across all of them: a diet that produces impressive growth in a juvenile is producing damage in an adult.

Weigh the animal, not just the food. In a chelonian the weight trend is the health record.

Check the enclosure before you check the animal

Reptile appetite is a function of temperature, light and hydration before it is a function of anything else. Owners routinely arrive at the vet having considered every disease and not having measured a single temperature.

Temperature.
Measure the basking surface, the warm side, the cool side and, for aquatic species, the water, using a probe or infrared thermometer rather than a stick-on strip. Digestion, immune function and appetite all depend on the animal being able to reach its preferred body temperature. Enclosures drift over years: a lamp ages, a thermostat is nudged, the room changes use, a window is opened differently, or the animal is moved to a cooler spot.

Ultraviolet.
Ultraviolet B output falls progressively with hours of use and the lamp continues to produce visible light long after the useful output has gone. Without adequate ultraviolet, a chelonian cannot make vitamin D3, cannot use dietary calcium, and develops metabolic bone disease with lethargy and appetite loss among the earliest signs. Note the replacement date on the fitting rather than trusting appearance, and check whether the lamp is being filtered by glass or fine mesh, both of which block ultraviolet.

Basking access.
An aquatic turtle that cannot get fully out and dry off does not thermoregulate properly and develops shell problems. Check that the dock is accessible for an older, heavier or arthritic animal, because a ramp that worked at five years old may not work at twenty.

Water quality.
For aquatic species, poor water quality suppresses appetite and causes skin and shell disease. Filtration adequate for a juvenile is usually inadequate for the adult.

Season and photoperiod.
Shortening days reduce appetite in temperate species. Check whether the lighting schedule has been left on a summer setting or has drifted.

Why a mature chelonian stops eating

Once the enclosure has been checked and corrected, work through these.

Brumation preparation.
In temperate species, with a gradual reduction, in autumn, in an animal that is otherwise bright and holding weight. Requires a pre-brumation health assessment before proceeding.

Beak overgrowth or jaw problems.
An overgrown beak prevents the animal from cutting food. The tell is an animal that approaches food, attempts to take it and gives up, rather than one that ignores food entirely.

Vitamin A deficiency.
Common in aquatic turtles fed on muscle meat, dried shrimp or pale lettuce. It causes swelling of the eyelids, sometimes to the point where the animal cannot see, along with respiratory and skin changes. An animal that cannot see its food stops eating.

Respiratory infection.
Reduced basking, open-mouth breathing, bubbles at the nostrils, a stretched neck with each breath, and in aquatic species swimming lopsided. Appetite loss often comes before the obvious signs.

Renal disease and gout.
A significant problem in older tortoises, particularly those kept dry with poor drinking access over many years. Signs are vague: lethargy, weight loss, poor appetite, and sometimes swellings around joints.

Bladder stones.
Very common in tortoises and strongly associated with dehydration and with a diet high in protein and oxalate. They cause straining, blood, lethargy, appetite loss and, in females, difficulty laying.

Retained eggs.
Females produce eggs without a male. A female with nowhere suitable to dig, or with a stone or a pelvic problem obstructing her, becomes egg bound. Restlessness, digging and appetite loss are the pattern.

Liver disease.
Fatty liver in an obese animal, often the end point of years of overfeeding a growth diet.

Parasites.
Worth a faecal check in any animal losing condition, and mandatory before brumation.

Mouth infection.
Redness, plaques or a cheesy discharge in the mouth, sometimes with reluctance to eat firm food.

Cataracts and vision loss.
In genuinely old animals, and in some after cold damage. An animal that cannot see food may need it presented differently or by hand.

Arthritis.
Older animals move less, reach the food less, and lose out to competitors.

Competition and stress.
In shared enclosures, a subordinate animal may be excluded from the basking site or the food. Basking site competition is a common and underrecognised cause of a single animal declining in a group.

For grazing species, hay and grasses should be the bulk of the diet, not a decoration around a bowl of salad.

Feeding an older animal well

Reduce frequency, not just quantity.
Adults do not need to eat daily. An older animal with slowing metabolism needs less than it did while it was growing, and continuing juvenile portions is the commonest way an adult chelonian becomes obese.

Increase fibre and reduce protein.
For herbivorous tortoises this means grasses, hay and weeds as the base. For maturing aquatic turtles it means shifting from an animal-protein diet towards greens and aquatic plants.

Keep the calcium supply appropriate.
Cuttlefish bone available for tortoises, and a calcium supplement used as directed for the species and the ultraviolet setup. Calcium without ultraviolet or dietary D3 achieves little, which is why the lamp and the supplement are one decision rather than two.

Take hydration seriously.
Chronic low-level dehydration over years is a major contributor to bladder stones and renal disease. Regular shallow lukewarm soaks, a water source the animal can actually reach and get into, and appropriate humidity for the species all matter more with age, not less.

Present food so an older animal can reach it.
Lower dishes, an accessible basking platform, food in more than one place in a shared enclosure, and hand feeding if vision is failing.

Do not use appetite stimulation as a substitute for diagnosis.
Warming an animal up and offering a favourite food will often produce a meal, which is useful supportive care and tells you nothing about why it stopped.

What the vet will ask for

• Species, approximate age, and how long you have had the animal.
• Current weight and shell length, and the trend over as long a period as you have.
• Measured temperatures at each site, and how they were measured.
• Ultraviolet lamp type, distance, whether it passes through glass or mesh, and the replacement date.
• The exact diet: every item offered, the proportions and the frequency.
• Any supplement used, and how often.
• Droppings and urate appearance and frequency.
• Water source and how often the animal drinks or soaks.
• For females, whether she has laid before, and any digging behaviour.
• Whether the animal has ever been brumated, and how.
• Whether other animals share the enclosure.

Expect blood work in an older animal, because renal disease and gout are diagnosed on chemistry rather than on appearance, and expect imaging if a bladder stone or retained eggs are possible. Both are common enough in mature chelonians that they are checked routinely rather than exceptionally.

What never to do

Do not feed dog food, cat food, bread, dairy or processed human food to a tortoise.

Do not build a herbivorous tortoise's diet around fruit.

Do not continue a juvenile feeding schedule into adulthood.

Do not assume an ultraviolet lamp works because it lights up.

Do not brumate an animal that is underweight, unwell, or has not been assessed.

Do not brumate a tropical species at all.

Do not use a refrigerator or an unheated outbuilding for brumation without a specific plan agreed with a vet.

Do not attribute appetite loss to age. In a species that lives for decades, age is rarely the answer.

Do not soak a weak animal unattended, and never in deep water.

A steady weight, regular droppings and normal basking behaviour are what a well-fed adult chelonian looks like.

When to get help

Contact a reptile vet the same day for an animal that is not eating and not basking, open-mouth breathing or bubbling at the nostrils, straining, blood in the water or urates, swollen eyelids that prevent vision, or collapse.

Book within the week for weight loss over consecutive weighings, an overgrown beak, a change in dropping or urate appearance, an adult that is still growing rapidly, or any tortoise you intend to brumate.

Bring the weight and length record, the measured temperatures, the ultraviolet lamp details and replacement date, and the full diet by proportion. In chelonian medicine the husbandry record usually identifies the cause faster than examining the animal does, and the animal itself gives very little away.