Influence of foraging ecology on alimentary tract size and function of Svalbard reindeer

Abstract

Insular, high arctic Svalbard reindeer (Rangifer rarandus platyrhnchus) appear better adapted to digesting grasses, sedges, and mosses than mainland reindeer and caribou (R. t. tarandu, R. t. granti, R. t. groenlandicus). We investigated the extent to which dietary differences are related to alimentary tract morphology and function. Concentration gradients of nutrients in the alimentary tract of Svalbard reindeer follow a similar pattern to that found in Norwegian domestic reindeer. Alimentary pools sizes of total digesta, water, Na, K, and P increased with body weight, and the rumen–reticulum dominated as the major compartment of the alimentary tract. In Svalbard reindeer, cecal nutrient pool sizes were relatively larger in winter than summer (P < 0.05) for all nutrients except P. Relative weight of cecal contents (% body weight) of Svalbard reindeer exceeded that of Norwegian reindeer in summer, and a further significant increase (P < 0.05) was noted in winter. Volatile fatty acid levels and molar proportions in Svalbard reindeer suggest low cellulolytic activity in the rumen and high fiber, low sugar fermentation in the cecum. The relatively large winter cecum size in Svalbard reindeer modulates the seasonal decline in volatile fatty acid production and allows for high rates of nonprotein N, water, and mineral absorption. Results support the "grazer" hypothesis applied to Svalbard reindeer in the winter period, but not in summer.