Investigations on the use of chromium oxide as an inert external marker in captive Asian elephants (Elephas maximus). Passage and recovery rates

Digestibility studies in zoo herbivores that are kept in groups are often confounded by the fact that the intake of hay, which is usually offered to the whole group, cannot be measured on an individual basis. This problem can be solved by using a double marker method with an internal and an external marker. In elephants, the internal marker lignin has repeatedly been used successfully; however, no external digestibility marker has been reliably established for this species. Seven captive Asian elephants were fed 500 g of chromium oxide per animal as a pulse-dose. Faeces were collected in toto for 60 hours afterwards. The amount of faeces from each single defecation was weighed, and a representative subsample was taken for chromium analysis. All faeces defecated during night hours were treated as a single defecation unit. With the individual chromium concentrations and the total weights, the recoveries of the chromium marker could be calculated, and the passage rates for these animals were determined. Additionally, four animals in an elephant orphanage in Sri Lanka were fed the same amount of chromium oxide. For these animals, only the passage rates could be determined. The average first marker appearance was 24 hours, and the average last marker excretion 54 hours after marker feeding. The average mean retention time for four adult animals was 31.7 ± 2.7 hours. On average, the elephants excreted 3.9 ± 1.2 kg faeces/100 kg of body mass per day. The average chromium oxide recovery was 97 %. The results confirm that chromium oxide is a reliable external marker in Asian elephants. The passage rate data compares well with other data from the literature. Like perossidactyls, the elephant uses a digestive strategy of passing large amounts of low quality forage through its gut within a relatively short period of time.