The importance of calcium in relation to phosphorus, especially in folivorous reptiles.

The green iguana (Iguana iguana) is being employed for this presentation because it is paradigmatic of a large, showy, intelligent (for a triune-brained reptile), rapidly growing, folivorous lizard taxon that is displayed in many zoological collections. Green iguanas are very favoured by the pet trade (approximately one million are imported into the USA annually, and nearly an equal number are imported into and distributed to the UK, continental Europe, and Asia). Even with trade, green iguanas are still relatively nonendangered over much of their range because captive breeding is often effective. Loss of habitat, however, still threatens some native populations. Green iguanas are easy animals to husband and treat because they are relatively large and can be handled with minimal physical restraint by experienced personnel, blood samples can be readily obtained without deleterious consequences, and an ever-increasing body of data that documents the normal physiological chemistry values of both healthy and sick iguanas is being accumulated. With proper nutrition and husbandry, green iguanas grow to mature size (although not always full sexual maturity) under captive conditions in about 2-2.5 years; in the wild, adult size and sexual maturity requires an additional 1-2 years (Rodda, 1992). Nutritionally-adequate and readily-acceptable food usually can be grown locally or obtained at most greengrocers’ fresh vegetable counters (an important consideration when animals are being kept in captivity). Some iguanas tolerate less than ideal diets, often sustaining only modest permanent injury if the harmful diet is corrected before skeletal growth has ceased. Growing iguanas require a well-balanced diet that contains adequate Ca without concomitant excessive P (the reasons for this are complex), but simply stated, Ca is essential for the following physiological processes: