Structure and Function of the Digestive Tract of a Herbivorous Lizard Iguana iguana

The green iguana, Iguana iguana, is herbivorous throughout life and utilizes a microbial fermentation system in the elaborated hindgut to degrade plant fiber. Iguanas degrade hemicellulose and cellulose approximately as effectively as their mammalian counterparts: mean NDF (total cell wall fiber) digestibility in food with a lignification index of 18 was 54%, compared with a mean of 60% in ruminant mammals. Iguanas also extract leaf protein effectively: protein true digestibility averaged 86%, compared with 89% in ruminants and 88% in nonruminants. Volatile fatty acids (VFAs), the products of fiber fermentation used by the herbivore for energy, were detected in the hindgut organs of Iguana in concentrations similar to those in the rumen of cattle (807 vs. 876 μmol/g dry mass). The individual digestive organs maintain their relative proportions through ontogeny, and the ratio of digestive tract capacity to net body mass is the same in growing and mature iguanas. Contrary to previous assertions, reptiles can be as efficient herbivores as mammals.