DIET AND NUTRITION

Diet and Nutrition: Inner_about

IN THE WILD

The Green Iguana (Iguana iguana) is an obligatory herbivorous reptile native to central to southern America (Carothers, 1984; Troyer, 1984; van Marken Lichtenbelt 1993, 1992).

Green Iguanas are a generalist species, and almost entirely folivorous (Rand et al., 1990) with the stomach contents of individuals from Panama being found to contain numerous species of bushes, herbs, tree and vine leaves, and in some cases fruits, though these are far less commonly found, and likely only consumed accidentally while eating the leaves (Rand et al., 1990).

This high foliage diet is possible because the Green Iguana has a highly developed hind gut to maximise efficiency in digesting carbohydrates, such as cellulose (Ilverson, 1982; McBee and McBee, 1982). This developed hind gut contains microbial cultures, cultivated with the specific purpose of fermenting fibrous plants. This gives the iguana a similar capability for digesting plant matter to that of a mammalian ruminant, as particularly indicated by the finding of volatile fatty acids (VFAs) as similar levels to cattle with 807μmol/g dry mass in the iguana against the cattle's 876. These VFAs are the source of energy in herbivorous species, and the product of fermenting high fibre plant matter (Troyer, 1984).

Green iguanas require an average of 71.7 kJ of energy per kg per day throughout the year in both males and females. In a year 15% of the female's energy is devoted to egg production. Majority of this energy is spent on locomotion, which males perform more of during the breeding season (van Marken Lichtenbelt et al., 1993). This explains the decrease in wild male's body condition during the mating period of March-April and for the females the oviposition period of May-June (van Marken Lichtenbelt et al., 1993).

As for water uptake, the Green Iguana will get most of what it needs from its diet, but can drink from pools of water when necessary, or during the dry season they will eat flowers to increase the amount of water they take in (van Marken Lichtenbelt, 1993).

CAPTIVITY

WHAT TO FEED GREEN IGUANAS?

Foods available for captive animals are often much lower in nutrients than the animals requirements, often needing supplementation. The most crucial mineral reptilian diets may be supplemented with is calcium, necessary for healthy bones and eggs. If the diet does not contain enough calcium then the large weight of a green iguana, coupled with its climbing nature can lead to the fracturing of bones (Donahue, 1996). The calcium, however, must be balanced against the phosphorus intake with a balance of approximately 2.5:1 Ca:P (Anderson and Capen, 1976). Donahue (1996) suggests calcium should make up 1% of the dry matter portion of the diet, though this is based on endotherm requirements as ectotherm data is sparse. The other major components to focus on in green iguana are proteins and fibers (Donahue, 1996). In juvenile green iguana, fibre can inhibit their ability to grow, and as such should be proportionally low in their diets (Donahue 1996). During the breeding season, however, females involved in breeding programs require high protein in their diet for egg production (van Marken Lichtenbelt 1993).

Based on this information and the approximate nutritional information of these ingredients provided by Donahue (1996) a diet consisting of romaine, iceberg lettuce and spinach has been concocted and it's nutritional information can be found in the table below. The diet should be presented to the iguana on a daily basis, each morning, to allow them to exhibit their natural foraging behaviour throughout the day each day (Donahue 1996, EAZA 2014, van Marken Lichtenbelt et al. 1993).

NUTRIENT CONTENT

BENEFITS

This single diet is practical and extremely versatile for green iguanas. The first thing to note is the calcium:phosphorus ratio is 2.45:1, this makes it extremely close to the 2.5;1 recommendation by Anderson and Capen (1976), avoiding the need for supplementation in this basal diet. At the same time, the calcium portion of the diet is indeed following the 1% suggestion by Donahue (1996). Secondly, van Marken Lichtenbelt et al. (1993) energetic requirement of 71.7kJ/kg/day is exceeded in this diet, providing the iguana the energy to perform its full wild behavioural routine, however, if the iguana is relatively inactive and begins to put on weight the spinach can be removed from the diet to significantly reduce energy intake while having minimal impact on the other nutrient and mineral compositions.

In the cases of juveniles and breeding females, this same diet should also be highly functional. It contains a low proportion of fibre, avoiding inhibition of juvenile gastrointestinal tracts (Donahue 1996) and high levels of protein, usable by females for egg production (van Marken Lichtenbelt et al. 1993). As a side note to this, a phosphorus-free calcium dust can be added to the diet if the shells of the eggs she produces are found to be too weak. Similarly, if the heat lamp provided is not providing an appropriate level of UVB then vitamin D supplementation may also be incorporated.

Finally, and perhaps most simply, the diet consists entirely of foliage of sorts, matching the green iguana's primary food type in the wild (Carothers, 1984; Troyer, 1984; van Marken Lichtenbelt 1993, 1992), allowing them to retain some degree of wild foraging capability.

DIET MANAGEMENT

The immediate issue with feeding the iguana on this diet is that, if kept with another individual, it is difficult to ensure they eat the amount of each nutrient that they are supposed to. This could potentially be remedied by training the individuals to only feed from separate locations, but this would contradict EAZA (2014) guidelines that state that, as much as possible, unnatural behaviours should not be encouraged in captive animals, training for this should therefore be a last resort.

Another issue is that, much like humans, iguanas have individual preferences (Donahue 1996). This can cause problems with having the animals ingest the correct amounts of each nutrient. For example: a juvenile iguana may dislike romaine and avoid consuming it, while continuing to eat the spinach and iceberg. This excludes the portion of the diet that is providing the most energy, and focusing more on the spinach which has a higher proportion of fibre, which could impact on the juvenile's digestive system (Donahue 1996).

A positive side to managing this diet, however, is that all the ingredients are readily available in most supermarkets. With this in mind, and considering the short lifespan of all vegetation, even when refrigerated, it may prove beneficial to meet the local supermarket with a deal whereby the zoo would receive discounts on romaine, iceberg lettuce and spinach in exchange for publicity for the supermarket, highlighting their support for the zoo (for example). The zoo may also be able to acquire ingredients that are beyond the sell by dates as the supermarkets are then unable to sell them anyway.

Preparation of the ingredients would not take a long time, no matter how much the animal requires. All leaves would need rinsing. Spinach leaves are small enough to be fed whole to an adult iguana, while the romaine and iceberg lettuce need only a small amount of chopping. For juveniles all the food should be chopped to avoid choking hazards, however, as they need much less than the adults (based on weight), it would take less time to prepare anyway. All ingredients need to be weighed to ensure the balance between them is correct.