| Sixty steers were utilized to determine the effect of feeding high oil corn on performance, diet digestibility and carcass composition. Feeding high oil corn decreased intake, but did not affect average daily gain or feed efficiency. Ration digestibility of dry matter, gross energy, and starch were increased with high oil corn. Marbling score and quality grade of cattle fed high oil corn were higher than cattle fed control corn. Feeding high oil corn also tended to increase polyunsaturated and decrease saturated fatty acids in the longissimus muscle. Forty beef steers were used to determine the effects of corn hybrid, maturity at harvest, and processing on digestion characteristics of corn silage. Processing increased intake of hybrid 3489 but did not affect intake of hybrid 3335. Harvesting silage at blacklayer maturity decreased dry matter, starch, NDF and ADF digestibility when compared to harvesting silage at ½ milkline. Starch digestibility was greater for 3335 than 3489. Processing increased starch digestibility but decreased fiber digestibility for all maturity and hybrid combinations. The usefulness of natural abundance levels of stable carbon and nitrogen isotopes as microbial markers was assessed in a third study. Rumen bacteria were naturally labeled with a carbon isotope ratio typical of C3 plants and a low stable nitrogen ratio typical of alfalfa. In situ samples of processed and unprocessed corn silage (C 4 plant with greater 13C and 15N ratios than diet or ruminal bacteria) were ruminally incubated to determine if microbial attachment could be determined using the stable isotope ratios. Nitrogen isotope ratios of in situ residues declined linearly across incubation times (0 to 24 h). Processed silage declined more rapidly than unprocessed silage suggesting more extensive microbial colonization. Stable carbon isotope ratios showed similar responses; however, increased variability prevented detection of differences between the processed and unprocessed silage. |
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