Part 1: The Relevant Nature of Sloths

Part 1: The Relevant Nature of Sloths
By Assoc. Prof. Dr. Somphote Weerakul (Ajarn Kaew)

I once published an article about sloths. Every time I write about them, it is because I have encountered health issues in practice. This time, I would like to continue the discussion. Gastrointestinal diseases remain the number one health issue among exotic pets, mostly stemming from dietary and management problems. Unlike common pets—where diarrhea is usually caused by food poisoning, scavenging through trash, or foodborne infections—herbivores typically suffer from diarrhea or bloating due to an inappropriate dietary ratio.

Dietary Habits and Metabolism
Sloths are primarily folivores (leaf-eaters), consuming shoots, flowers, and occasionally fruits depending on the species. If given the chance, they may also eat insects, eggs, and small animals. Algae growth on the fur of some sloth species is sometimes thought to be a food source, but this might simply be a grooming behavior, as algae have not been detected in their digestive tracts (The Sloth Conservation Foundation).

This diverse diet is usually found in two-toed sloths (Choloepus). Three-toed sloths (Bradypus), however, have a much more restricted and specific diet. They mainly selectively eat Cecropia leaves, and occasionally Clethra and Clusia leaves. This makes them difficult to keep in captivity, turning diet into a major health issue.

Sloths are slow-moving animals with little muscle mass and a very low metabolic rate. Owners must be aware of this because it directly correlates with disease development and treatment approaches. A sloth's diet should be low in energy and low in protein—even though the nutritional levels of leaves (energy, protein, fat, and carbohydrates) are generally richer than grass. However, dietary fiber must remain high.

The diet must consist of both:

Soluble fiber (pectin, hemicellulose): Ranges from moderately digestible to hard-to-digest.
Insoluble fiber (cellulose and lignin): Hard-to-digest and indigestible, respectively.
Digestible fiber is the primary source of food and energy for herbivores, including sloths, rather than starch, protein, or fat. Furthermore, there must be a high enough proportion of indigestible fiber to stimulate normal excretion and bowel movements. Their required energy level is significantly lower than other animals, sitting at only 37-45% of the Basal Metabolic Rate (BMR)—a reduction of more than half.

Digestive Anatomy and Microbial Fermentation
Because they are herbivores, their foregut is divided into compartments similar to a camel's, but with more than six chambers (multichambered). The digestion mechanism is similar to a cow's: it relies on microbial fermentation of the ingested food. Therefore, the initial food source is crucial for proper fermentation and maintaining microbial balance.

To put it another way, sloths rely on microbes for fermentation and digestion. The sloth chooses food suitable for the microbes, and the microbes ferment it, turning it into the body's main source of nutrients and energy. The microbes themselves also benefit from this food to grow. If a sloth eats an unnatural diet or the owner feeds it improperly, it disrupts the microbial balance and harms the digestive tract. Even before outward symptoms appear, the mechanisms of intestinal inflammation have already begun.

The anatomy of their stomach and digestive tract prevents sloths from burping, vomiting, or even passing gas. This can lead to massive gas accumulation if they receive an improper diet, making dietary management absolutely critical. Veterinarians must understand diagnostic and treatment approaches that align with these unique traits. A large amount of gas is often found in captive sloths, waiting to be expelled only through defecation, which happens infrequently (only about once a week in nature). Feces are stored in the large intestine and excreted in massive quantities, sometimes making up to 30% of their body weight.

Transit Time and Defecation
Another vital factor affecting treatment is their extremely slow and unpredictable gastrointestinal transit time. Beyond their low metabolic rate and muscle mass, this transit time is believed to depend on diet, light, and temperature.

Note on Temperature: Sloths are poor at regulating their body temperature, acting almost like cold-blooded animals. They try to maintain a low body temperature (30-34°C) to conserve energy. Bradypus sloths forage throughout the night, while Choloepus sloths forage periodically during the day. Overly cold temperatures slow down microbial activity in the gut and reduce microbial populations. Sick sloths are often given probiotics, as microbes digest better in warm conditions, which also encourages the sloth to eat slightly more.
Habitat and social factors also influence their eating habits. In typical herbivores, the process from ingestion, fermentation, absorption, to excretion takes about half a day:

Rabbits: 4-6 hours (hard feces) and 8-12 hours (soft feces)
Guinea pigs: 3-5 hours
Horses & Cows: 24-72 hours
Elephants: 18-48 hours
Sloths: A week to a month
This incredibly long timeline also relates to the very small volume of food they eat each day. For example, three-toed sloths eat only 2.5 ounces (73.5 grams) of leaves per day. Microbial fermentation is highly thorough because it takes so long. Tests by the Sloth Conservation Foundation in Costa Rica found that fermentation takes 11-30 days (averaging 16 days).

If we evaluate the undigested matter excreted as feces, it accounts for about 20% of the ingested food (based on lignin and cellulose in Cecropia leaves), or perhaps over 45% if evaluated by Neutral Detergent Fiber (NDF) levels (36% to over 60%). The long fermentation period allows microbes to fully utilize dietary fiber, resulting in a high digestion coefficient. While individual fecal pellets are small and look like deer pellets, sloths accumulate them in the distal large intestine before passing them all at once.

Nutritional Guidelines vs. Captive Diets
When evaluating natural nutritional values (using Cecropia leaves as an example), they contain roughly 1.13% protein, 0.46% fat, and 32.7% carbohydrates. Overall, this is a low-energy diet, but it is rich in minerals such as magnesium, potassium, manganese, and iron.

However, looking at the AZA (Association of Zoos and Aquariums) Sloth Nutrition Guide, it states that sloths eat nearly 100% leaves. Yet, most of their recommended captive diets have high protein levels of 15-25% (whereas natural leaves contain about 10%). The diet should be high in fiber, with NDF levels around 10-30% and Acid Detergent Fiber (ADF - lignin, cellulose) at 5-15%. To prevent ileus and colic, ADF should ideally be even higher (up to 25-30%), though specific research on sloths is still lacking. Clinical studies showing the correlation between diarrhea and improper diet strongly support this.

The AZA recommends that starch and sugar be kept under 15%, though ideally, it should be even lower, utilizing only naturally occurring starches in leaves. Sugary items should be reserved strictly for training or behavioral enrichment.

Dietary Risks in Captivity
I suggest taking captive guidelines with caution. The high prevalence of sloth diarrhea often stems from misunderstandings regarding these nutritional needs. Sloths derive their energy from microbial fermentation, making it strictly necessary to limit starch and sugar.

The Sloth Conservation Foundation notes that many captive sloths live far from their native tropical rainforests, making it difficult to forage for their natural plants. As a result, many organizations feed sloths whatever is available: vegetables, root crops, and plants from non-tropical climates—foods they have not evolved to digest. Therefore, the diets compiled by the AZA are not completely natural but are adapted out of necessity.

The typical diet for captive two-toed sloths often includes boiled carrots, eggs, flowers, celery, green beans, and bananas. This contains far too much glucose for a sloth and can lead to health complications like diabetes and heart disease. Clinically, however, the very first health issue you will encounter is diarrhea, which can be severe enough to cause death.

Recommended Natural Plant Species
Leaves recommended by the AZA include hibiscus, bamboo, Cecropia, copperleaf, elm, mulberry, plumbago, and willow.

Natural surveys by the Sloth Conservation Foundation found many additional species:

For three-toed sloths (strict folivores): Cocoa pods and leaves (Theobroma cacao), sangrillo (Pterocarpus officinalis), Cecropia spp., colorado (Luehea seemannii), chilamate (Ficus insipida), Micropholis venulosa, fig trees (Ficus spp.), Mandevilla sp., and families Moraceae, Euphorbiaceae, and Bombacaceae.
For two-toed sloths (varied diet): Flowers from the Bombacaceae family, leaves and flowers of the barrigon tree (Pseudobombax septenatum), vines, espave (Anacardium excelsum), poro (Cochlospermum vitifolium), and jobo (Spondias spp.).
There is still a lot more to cover regarding diarrhea. Please stay tuned for the next part on how it happens and how it should be managed.