It is believed that sloths have the slowest digestive rate of any mammal, but the true rate of food passage from ingestion to excretion is still debated. In 1978 Montgomery and Sunquist claimed the rate of digestion in the three-fingered sloth to be the slowest recorded for any herbivorous mammal, with 50 days being taken for the passage of 95% of 3mm glass beads. But it is highly unlikely that these beads would have passed through the sloths many stomachs in the same manner as their natural diet would. It is thought that the beads probably became lodged in the pre-pyloric stomach, lengthening the retention time.
The key to understanding the sloths slow pace is through their low metabolic rate and extremely low-energy diet. In order for the Sloth Sanctuary to develop and improve their rescue, rehabilitation and hand-rearing practices, it is essential that we have a scientific understanding of these factors. Sloth Sanctuary biologist Rebecca Cliffe measured how temperature affects the rate of food passage in the three-fingered sloth using the digestive marker Carmine Red. Carmine Red is a harmless, indigestible faecal marker derived from the female Cochineal insect.
After 23 trials, the rate of digestion was found to vary between 11 and 30 days, with an overall average of 16 days being taken for the passage of the carmine marker. This is by far the longest digestive rate recorded for any mammal and is the key behind understanding why sloths are so slow!