Digestibility of Plant Constitutents By Canada Geese and Atlantic Brant

Abstract

The ability of free—ranging Brant (Branta bernicla) and free ranging and captive Canada Geese (B. canadensis) to digest various constituents of marsh plants was studied using lignin as a nondigestible tracer in plant food and feces. These constituents included total organic matter, soluble carbohydrates, protein, total ether—soluble material, soluble phenolics, cell wall polysaccharides, and phenolic acids esterified to plant cell walls. The digestion of total organic matter averaged 37% in both species of geese, indicating that geese are less efficient at digesting plant material than most other vertebrate herbivores. The low total organic matter digestion was largely a result of inefficient digestion of cell wall polysaccharides. Geese digested °28% of the cellulose and 25% of the hemicelluloses present in their plant food. In contrast, the apparent digestibility of soluble carbohydrates were 69—85%, and the digestibility of protein (61—80%) was similar to that of most other vertebrate herbivores or graminoid diets. The two cells wall polysaccharides still provide up to 31% of the energy geese extract from plants despite their low digestibility, because they are present in relatively high concentrations (together, °40% of dry mass). Geese digested cellulose as efficiently as predicted by the previously reported relationship between herbivore body size (or metabolic requirement) and cellulose digestion.