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Evaluation of changes in nutritional quality of corn residue throughout grazing period
Residues of corn (Zea mays) have successfully been utilized as an economical roughage and energy source for ruminants. Corn plants from two hybrids (102 and 119 d maturity) were planted at two different planting dates (April 27 and May 27) and harvested at periodic intervals from September 2012 to December 2012 in order to determine changes in quality and proportion of corn residue as the plant dries and is exposed to effects of weathering. Plants were separated into stem, blade/sheath, husk/shank, cob and grain, and analyzed for dry matter (DM), neutral detergent fiber (NDF) and total digestible nutrients (TDN). Estimates of TDN were derived from NDF and in situ NDF digestibility assuming 100% digestibility from the soluble fraction and 12% metabolic loss. Hybrid did not influence the proportion of plant components (P > 0.40) even though it tended to influence the NDF and TDN of the residue (P < 0.10). Percentage of DM in each plant part increased until the November sampling date for both hybrids and planting dates and then began to decline (P< 0.01). Grain, as a percentage of the total plant DM, tended to increase to approximately 60% where it then remained relatively constant for both planting dates and hybrids (P < 0.15). Proportions of stem, blade/sheath, husk/shank and cob made up smaller components of total plant DM as it matured with the largest relative reduction occurring in the blade/sheath or stem. A linear increase over time for NDF was observed for both hybrids in the May-planted plot (P < 0.01) whereas NDF content of the stem and husk/shank decreased in the April-planted plot (P < 0.01). Hybrid had an impact on TDN values (P < 0.01) primarily because the 119 d hybrid was less mature at the early sampling dates. In both plots, TDN of husk/shank remained constant (P > 0.40) while cob decreased (P< 0.10). Corn hybrid, planting date and plant component affect the quality of residue ruminants will be consuming at a certain time point during the grazing season. However, plant maturity appears to be the largest factor in determining residue quality.
Keywords: corn residue, plant components, forage quality