FiberA classification of carbohydrates based on their in-digestibility by animal enzymes. This includes many types of carbohydrates such as cellulose, hemicellulose, lignin and pectin. More simply, insoluble fiber can be thought of as the cell walls of plants. These cell walls provide rigidity and structure to the plant and are thus hard to "break apart" in digestion.
Fiber is of special concern to reptiles that eat vegetables and fruit as a large portion of their diet. Bacteria in the digestive system uses fiber to create vital nutrients for the reptile that cannot be sourced from any other part of the diet. In herbivores, this includes vitamin B12. However, it is important not to forget that bacteria exist in the digestive tract of all animals and play an important role in immune function and overall health. |
Purpose of Fiber |
Fiber has a variety of purposes that mainly depend on the digestive system of the reptile. In carnivores and insectivores, fiber has little purpose beyond keeping the digestive system regular and adding mass to the stool. It can also play a role in feeding good bacteria so that bad bacteria don't colonize the gut.
However in herbivores the role of fiber is crucial. Bacteria break down fiber into compounds called volatile fatty acids. These provide an energy source for the enterocytes (the cells that absorb nutrients into the body) in the intestine. This energy source aids the enterocytes, which in turn aids intestinal health and nutrient absorption. Excess volatile fatty acids can be used by the reptile as energy. This is considered to be a large portion of the energy that herbivorous reptiles get from their food. Soluble fiber has a slightly different role than other fibers. Soluble fiber slows the absorption of food, preventing glucose spikes and diabetes. It also plays a role in trapping any excess cholesterol. The digestive system expels cholesterol into the gut, which can then be absorbed by soluble fiber to lower overall cholesterol. This is especially important in obese animals or animals prone to fatty liver disease. |
Prebiotics |
Prebiotics are foods that are digested by bacteria in the hind gut. Most fiber is a type of prebiotic, but the term usually refers to oligosaccharides . These are nutrients that interact with bacteria on a chemical level, preventing them from binding with the intestinal mucosa. This prevents diseases form colonizing the intestine and changes how bacteria interact in the hind gut. There has also been research suggesting that adding oligosaccharides to the diet increases the absorption of minerals, such as calcium, in the hind gut. Dandelion greens are an excellent source of oligosaccharides for plant eating reptiles.
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Fiber Requirements |
Requirements for fiber of individual species are not very well studied beyond a handful of galapagos turtle species. For a carnivore or insectivore, the fiber they consume when eating whole animal or insect prey is generally considered enough to sustain them. This is just one reason properly gut loading insects is so vital.
Herbivorous reptiles contain a specialize region of the hind gut called the cecum. This area is specially designed to ferment fiber. The cecum as well as the proximal colon of herbivorous reptiles has mucosal folds in order to increase surface area and slow digestion down. The merck veterinary manual recommends a crude fiber intake for omnivorous reptiles to be 20%-35%, however this number is extremely high when compared to other fiber level recommendations. Donoghue and Langenberg (1996) state that grazing galapagos tortoises, similar in diet to the leopard and sulcata tortoises, need about 12% crude fiber in their diet. These same tortoises showed a 41% cellulose digestibility, indicating that a large portion of their energy intake is indeed from fiber. Iguanas are recommended to consume between 6%-10% crude fiber by Allen and Oftedale (2003). Higher fiber diets have shown to slow growth in juvenile animals, but are likely not harmful. |
Testing for Fiber |
Most types of fiber are grouped together by how they are scientifically analyzed. This is because the methods to analyze fiber are not very precise. When talking about fiber content of foods, it is important to make sure you understand which type of fiber analysis is being used.
Dietary Fiber (seen on human nutritional labels) -Includes soluble fiber, insoluble fiber and about 15% of the inulin content -Enzymes are used to digest the carbohydrate material of a food. Whatever isn't digested is considered "dietary fiber." Insoluble Fiber -Includes cellulose, lignin and some hemicelluloses -Filter the digested solution from the dietary fiber test. Weigh what is filtered out. Soluble Fiber -Includes pectins, gums, mucilages and some hemicelluloses -Whatever is not filtered out from the insoluble fiber test Crude Fiber (seen on animal food labels) -A legally required fiber test that poorly estimates cellulose and other fiber content -An acidic and an alkali solution are used to filter away everything except for some fiber. This test is roughly equivalent to about 2/3 of the acid detergent fiber when testing foods commonly fed to reptiles, such as leafy greens. Neutral Detergent Fiber -Includes cellulose, hemicellulose and lignin -A neutral detergent solution removes everything from the sample except the fibers listed above Acid Detergent Fiber -Includes cellulose and lignin -An acidic detergent solution removes everything from the sample except cellulose and lignin |
Sources |
Allen, Mary E. and Olav T. Oftedale. Nutrition in Captivity. Biology, Husbandry and Medicine of the Green Iguana. 4:47-74 (2003).
Cheeke, Peter R. and Ellen D. Dierenfeld. Comparative Animal Nutrition and Metabolism. (2010). Donoghue, Susan and Julie Langenberg. Nutrition. Reptile Medicine And Surgery 1st Ed. 14:148-174 (1996) Nijboer, Joeke. Ed. Nutrition in Reptiles. Merck Veterinary Manual. 2015 Stevens, C. Edward and Ian D. Hume. Contributions of Microbes in Vertebrate Gastrointestinal Tract to Production and Conservation of Nutrients. Physiological Reviews. 78(2):393-427 (1998). https://www.megazyme.com/resources/dietary-fiber/measurement-of-dietary-fiber |