Estimating faecal output in reindeer during winter

Abstract

Faecal output (FO) was estimated indirectly in six penned male reindeer calves by use of intraruminal chromic oxide (Cr 2O 3) constant release capsules (CRCs) and compared with their actual FO, which was determined in a parallel study by use of total faecal collection (TFC) with faeces collecting bags. The captive animals successively ate two different diets: a diet of pelleted reindeer feed (RF-80) succeeded by a diet of mixed lichens. Using intraruminal CRCs to estimate FO resulted in 9.9 and 1.8 times overestimations of the FO of the animals on the RF-80 and the mixed lichen diet, respectively. The poor estimates of FO were probably caused by a faecal excretion rate of chromium that was lower than the capsule release rate given by the manufacturer of the capsules. Three of the reindeer calves were subsequently released into a free-ranging herd grazing at winter pasture. The FO of these calves and the FO of three free-ranging adult female reindeer was estimated by use of intraruminal CRCs. Actual FO was simultaneously measured in the calves by use of faeces collecting bags. Weight-specific estimates of FO was similar in free-ranging calves and adult females. The estimated and the actual FO were similar in the free-ranging calves, and the release rate of chromium from the CRCs was close to the release rate given by the manufacturer of the capsules in both calves and adult animals. It is concluded that the faecal excretion rate of chromium in reindeer being administered intraruminal CRCs depends upon the diet eaten by the animals. In future studies using intraruminal CRCs, the faecal excretion rate of marker should be measured under the trial conditions in a subset of animals to adjust marker estimates of faecal output.