Lichen polysaccharides and their relation to reindeer/caribou nutrition

Abstract

Samples of Cetraria islandica, Cetraria nivalis, Cladina stellaris,Cladina arbuscula, Cladina rangiferina and Stereocaulon paschalewere collected at 3 sites in 2 mountain areas in Norway. Alectoria ochroleuca was collected at 3 sites in 1 of the mountain areas. Lichens contained between 83 and 93% fiber, measured by the dietary fiber analysis, with Cladina spp. containing significantly more fiber than the other lichen species. The fiber consisted mainly of mannose, galactose, and glucose, but the relative content of each monosaccharide differed between species. Fibers from Cetraria spp.and Alectoria ochroleuca contained significantly more glucose than those from Cladina spp. and Stereocaulon paschale, while Cladina spp. and Stereocaulon paschale contained significantly more mannose and galactose. The higher glucose content in Cetraria spp. And Alectoria ochroleuca was reflected in a high lichenan content in these species, while the Cladina spp. and Stereocaulon paschale contained no lichenan. Solubility of the fiber fraction in hot water was strongly correlated to lichenan content, and great differences existed between species. Less than 5% of the dietary fiber was soluble in lichens of the Cladina genus, while more than 50% of the fiber was soluble in Cetraria islandica and Alectoria ochroleuca. Twenty-one percent of the dietary fiber was soluble in Cetraria nivalis. In vitro gas production experiments using rumen inocula from reindeer revealed a higher gas production rate the first 5 hours of incubation in Cetraria islandica, Cetraria nivalis, and in Alectoria ochroleuca compared to Cladina spp. and Stereocaulon paschale. Maximum production rate was observed at about 13 hours and dropped rapidly thereafter. No systematical differences in gas production rate between lichens species were observed after the initial phase. Differences in gas production rate in the initial phase resulted in higher total gas production in Cetraria islandica, Cetraria nivalis and in Alectoria ochroleuca compared to Cladina spp. and Stereocaulon paschale the first 9 hours of incubation. Total gas production after 52 hours of incubation did not vary between species. Gas production characteristics indicate that the amount of readily fermentable fraction was greater, whereas the amount slowly fermentable fraction was lower in lichens of the Cetraria genus and in Alectoria ochroleuca compared to Cladina spp. and Stereocaulon paschale. The water-soluble fraction is easy available for rumen micro-organisms and the results indicate a close relationship between high gas production in the initial phase and high proportion of water soluble fibers and/or lichenan content. Content, composition, and solubility of the fiber fraction could thus be potentially important factors determining nutritive value of the lichen for reindeer/caribou.