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Abstract
Cannulated beef cattle (four cows: 556 kg initial weight; four steers: 504 kg initial weight) were used in an experiment with two simultaneous Latin squares to determine effects of substituting alfalfa and(or) corn for vegetative bermudagrass (BER; 77% neutral detergent fibre and 5.5% acid detergent lignin) or mature bromegrass (BRO; 70% neutral detergent fibre and 6.6% acid detergent lignin) hay on digestion characteristics. For Controls, BER or BRO was fed at 1.32 or 1.54% body weight of cows and steers, respectively; other treatments entailed substitution for hay DM of alfalfa cubes (17%) or ground corn (33%). A protein supplement was given to all animals. In vitro neutral detergent fibre (NDF) digestion was slightly greater for BER than BRO. Supplement treatments did not affect the concentration of total volatile fatty acids or the molar proportion of propionate in ruminai fluid. True ruminai organic matter (OM) digestion was similar among diets; greater duodenal microbial OM flow and postruminal NDF digestion for BRO than BER diets were responsible for higher (P < 0.05) postruminal OM digestion for BRO diets. Supplement treatment did not affect duodenal microbial nitrogen flow or efficiency of microbial growth. Corn supplementation increased total tract OM digestion (P < 0.05). Alfalfa addition depressed total tract OM and NDF digestibilities more when added to BER than BRO; depressions in total tract NDF digestion with alfalfa and corn substitutions were additive. With constant DM intake, slightly less than ad libitum, alfalfa or corn substituted alone or together for hay did not improve characteristics of digestion by cattle consuming vegetative bermudagrass or mature bromegrass other than increased postruminal and total tract OM digestiblities with corn.
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