Effects of processing on digestible amino acids of corn hybrids for ruminants
Holthaus, Dennis L.
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Three experiments were designed and conducted to determine the effects of steamflaking com hybrids on the digestibility of essential amino acids, for use in more exact formulation of diets for cattle. Information on the digestibility of amino acids by cattle is very limited and could see immediate industry application. A series of experiments were conducted to measure the digestibility of lysine, methionine, threonine, dry matter and nitrogen content of four com hybrids. In the first experiment, one-hundred-twenty weanling rats were utilized in a 4 x 3 factorial to determine the digestibilty of the limiting amino acids for cattle. The rats were randomly assigned to individual wire bottom cages and fed one of twelve experimental diets containing one of four unprocessed corn hybrids supplemented with the ten essential amino acids except for the amino acid of interest. After seven days adaptation and seven days collection in the first trial, rats were rerandomized into a second trial with the source of com being steam-flaked. Amino acid profiles were determined by using HPLC. A follow-up experiment was then conducted to determine the rumen degradation of the limiting amino acids for cattle utilizing in vitro techniques of both processed (steam-flaked) and unprocessed grains incubated for 4, 8, and 16 h. The final experiment was conducted to determine the total tract digestion of lysine, methionine and threonine of the same steam-flaked hybrids in steers using a 4 x 4 latin square design. Total collection of feed, feces, urine and orts was used to determine the amino acid digestion, nitrogen retention and dry matter digestion. Differences (P <.05) were found for all variables measured between the processed and unprocessed grain sources when fed to rats. Lysine and methionine digestibility was the highest for Hybrid 2 and was significantly higher (P < .05)than all other hybrids. Hybrid 4 had the highest threonine digestibility and was greater than (P < .05) remaining hybrids. Digestion of methionine was higher (P < .05) than lysine or threonine and performance of rats fed the methionine deficient diets was greater (P < .05) than remaining amino acids. Dry matter digestibility in vitro tended to be higher for the steam-flaked grain when compared to the unprocessed grain.