Cathrine Dyhr Sauer (KU-LIFE), Jan Elnif (KU-LIFE), Mads Bertelsen
The main dietary nutrient for herbivorous species of animals is carbohydrates. The nutritionally most important carbohydrates are glucose, fructose, and the polysaccharides of starch, hemicellulose, and cellulose. The chemical bonds linking the monosaccharide units of hemicellulose and cellulose cannot be broken by digestive enzymes of vertebrate origin. Instead, hemicellulose, cellulose and partly starch are hydrolysed by fermentative microbes in herbivorous fore- or hindgut-fermenting species.
The green iguana (Iguana iguana) is a hindgut-fermenting lizard found in Central and South America. It is commonly kept in zoos and as personal pets. This herbivorous lizard can be difficult to feed in captivity, due to the limited variety and composition of available food items. Captive diets usually consist of a salad-type diet, potentially supplemented with pelleted feeds or a source of animal protein. The nutrient composition of produce is very different from wild counterparts, e.g., the fibre content of produce is much lower than the high fibre plant diet that iguanas have adapted to eat in the wild. The effects of feeding low fibre diets to iguanas are not well studied, but feeding with high amounts of easily fermentable carbohydrates is known to cause health problems in other herbivores species, such as horses and cattle.
To investigate the effects of feeding a diet high in starch (S-diet) relative to a diet high in fibre (F-diet), a feeding trial was conducted using 6 juvenile green iguanas. Iguanas were fed two different diets in a 2x2 cross over design. A 14 day adaptation period preceded the 24 day total faecal collection period. Faeces for each period was pooled and analysed for pH and nutrient composition (gross energy, dry matter, crude protein, crude fat, crude carbohydrate, crude fibre and sugar + starch). During the collection period, daily feed intakes were determined by weighing feed offered and feed residues. The iguanas were weighed at the beginning and end of each collection period.
There was no significant difference between the growth rate, feed conversion rate or daily dry matter intake (g DM/BW0.75) of the iguanas on the two diets. Faecal pH was significantly (P=0.001) lower on the S-diet (8.24±0.33) compared to the F-diet (9.13±0.11). Apparent digestibility of dry matter, crude protein, crude fat, crude carbohydrate and the sugar + starch fraction was significantly (all P<0.01) higher in the S-diet.