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Amino Acid Profiles of Heat-Damaged Grasses¹

Department of Dairy Science, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster 44691

W. L. Shockey

US Dairy Forage Research Center, US Department of Agriculture, Agricultural Research Service, Ohio Cluster, Wooster 44691

ABSTRACT

Orchardgrass was stored at 50% dry matter as large round bales to study short-term effects, and ryegrass (33% dry matter) was ensiled in laboratory silos, which were incubated at 35, 55, and 75°C for up to 46 d to study long-term effects of heat on the chemical composition of grasses. Bale temperature reached 70°C by d 6 postbaling and maintained that temperature for the remaining 7 d of the experiment. In the bales, concentrations of acid and neutral detergent insoluble nitrogen, acid detergent fiber, and lignin increased, whereas hemicellulose decreased over the 13-d storage. Concentration of total amino acids was 99.06 mg/g dry matter on d 0 and decreased linearly at the rate of 1.64 mg/g per d. Total nitrogen remained constant. Concentration of amino acids not soluble in acid detergent was 3.73 mg/g dry matter on d 0 and increased logarithmically (15%/d). Changes in chemical composition of the ryegrass stored at 75°C were similar to those of the orchardgrass. Composition of 35 and 55°C silage was not affected greatly by temperature. Concentration of total amino acids in fresh herbage was 55.86 mg/g dry matter and 47.08, 47.61, and 37.77 mg/g for the 35, 55, and 75°C silage after 46 d of storage. Amino acids insoluble in acid detergent constituted 7.2, 21.4, and 75.0% of the total amino acids in the 35, 55, and 75°C silage on d 46. In summary, heat damage reduced greatly the amount of amino acids present in the forages and altered their distribution.

¹ Salaries and research support provided by state and federal funds appropriated to the Ohio Agricultural Research and Development Center, Ohio State University. Journal Article Number 2-86.

² Department of Animal and Range Sciences, North Dakota State University, Fargo 58105.