The Nutritional Value of Browse to Moose

Abstract

Four tame moose (Alces alces) were used to measure the digestibility of browse and hay, retention time of digesta, and energy requirement during late winter. Digestibility of browse differed with species, twig diameter, and age of bark/wood tissue. Estimated digestibility of twigs cut at 2, 4, 6, 8, and 10 mm ranged from 50.4 to 29.3% in great willow (Salix caprea), from 45.5 to 27.7% in European mountain ash (Sorbus aucuparia), from 21.8 to 8.8% in silver birch (Betula pendula). Estimated digestibility of bark decreased from 47.2 to 31.2% and of wood from 44.5 to 18.3% when the most recent growth of mountain ash was compared to 2ndand 3rd-year growth. Rumen turnover time increased (r = -0.75, P < 0.05) with decreasing digestibility of browse. In vivo dry matter digestibility (DMD) of browse was significantly correlated (P < 0.01) to content of ash (r = 0.84) and more weakly to lignin (r = -0.74, P < 0.05). There was good correlation between DMD and in vitro dry matter disappearance (IVDMD) with rumen liquor from moose and from sheep (r = 0.86-0.96). Chemical content (proximate analysis) was highly correlated with IVDMD within each browse species (r = 0.91-0.99, P < 0.001). When different species were grouped, the correlation disappeared for all constituents except ash (r = 0.93, P < 0.001) and crude fiber (r = -0.65, P < 0.01). Assuming a 20% weight loss over winter, the estimated average daily intake of browse (at 47% DMD) by a 300-kg yearling moose (prewinter weight) would be 8.1 kg wet weight. J. WILDL. MANAGE. 46(2):333-343 Although there have been several investigations of the nutritive value of moose forage, none has used in vivo techniques on live moose. This paper reports the results of digestion trials on captive moose, and a comparison of several indirect methods of estimating apparent digestibility of browse. Five species of browse were investigated (preference according to Hagen 1958): great willow and European mountain ash, both of high preference, Scots pine (Pinus sylvestris), of medium preference, and common (Betula pubescens) and silver birch, both of low preference. To investigate if food intake by moose may be limited by slow digestibility of coarse feed, observations were made on rumen turnover time as a function of forage digestibility. Data on the energy balance of moose are few and partly contradictory (Gasaway and Coady 1974). To estimate energy requirements of our animals we measured changes in live weight and correlated this to daily feed intake. The work was supported by grants from The Norwegian Game Research Foundation and the Norwegian Agricultural Research Council. The authors are also in debt to I. Andersen, B. Skjevdal, L. Lordahl, and I. Lysne for their assistance and to students of the Norwegian University of Agriculture, who collected more than 1,000 kg of twigs for the digestion trials. We thank R. G. White of the University of Alaska for a critical review of the manuscript, and for allowing us to include some of his unpublished material.