The trophic ecology of Bison bison L. on shortgrass plains.
Study was in north-eastern Colorado with blue grama grass (Bouteloua gracilis) as the dominant species. Bison, cattle and sheep with an oesophageal fistula grazed at the rate of 1 or 3/12 ha and diet was sampled 6 times between December 1970 and October 1971. Percentage DM plant composition of the grazed fodder was analysed by microscope and plants were classed as warm-season or cool-season grass or forbs, or as shrubs. There were differences between seasons and animal species in plant composition, crude protein content and digestibility of diet. Bison were primarily grass-eaters, preferring warm-season grasses; they were less selective than cattle, fed in different areas and got less crude protein and their fodder was less digestible; they were better able to utilise the available fodder than cattle and they may have eaten more. Sheep ate fewer grasses than either bison or cattle. Each species selected a higher proportion of the plant groups that it could best digest.<new para>ADDITIONAL ABSTRACT:<new para>Seasonal data on dietary composition, grazing selectivity and forage digestibility were collected for bison, cattle and sheep on lightly grazed and heavily grazed shortgrass prairie where Bouteloua gracilis was dominant. Bison had a greater preference for warm-season grasses (B. gracilis, Aristida longiseta, Buchloe dactyloides, Muhlenbergia spp. and Sporobolus cryptandrus) than cattle and fed less selectively and in different areas; sheep consumed fewer grasses than either bison or cattle. Bison digested the warm-season grass component better than did cattle during winter, while cattle digested cool-season grasses better than bison throughout the year. Bison were considered more capable than cattle of fully exploiting the herbage resources of shortgrass plains.<new para>ADDITIONAL ABSTRACT:<new para>On poor quality forage, bison had a greater digestive power than cattle.