Accurate Amounts and Nutritive Values of Corn Residue

Abstract Text: Corn residues are becoming more important as roughage sources for beef cattle as conventional forage supplies decline.  Past research has assumed 10 corn plants yield a representative sample for nutrient analysis. This trial’s objectives were to determine variation among individual plants and re-evaluate energy and protein values of corn residues.  Samples were taken from an irrigated field in a corn, soybean rotation used for stalk grazing research for over 20 years.  There are non-grazed, fall grazed, and spring grazed areas (treatments) with 4 field replications of each.  In the fall of 2014, 10 consecutive corn plants were harvested from each of these field replications (3 treatments x 4 reps = 12 sampling locations).  Each of the 120 corn plants, harvested above the anchor roots just before grain harvest, was separated into grain, cob, leaf blade, leaf sheath, and husk.  Each plant part was dried (60°C) and DM amounts determined.  Statistical analysis was conducted using a model with 3 treatments and 4 replications, with corn plant as the experimental unit.  The analysis was repeated 10 times using 1 corn plant, 2 corn plants, etc. until all 10 were included. Grain yield was not affected by grazing treatment (P = 0.49).  As expected, all plants were not the same.  Overall grain yield ranged from 160 to 293 grams/plant.  The SEM declined as more plants were added to the analysis from 18 with 1 plant to 4 with 10 plants, minimal decline in SEM was observed as plants 6 to 10 were added to the analysis.   The average amount of leaf blade, leaf sheath, and husk was 23.8% of grain.  As numbers of plants were added to the analysis SEM declined from 1.5 at 1 plant to 0.4 at 10 plants, with minimal decline from 6 to 10 plants.  Leaf blades had 15.4% ash, therefore the amounts of digestible OM (DOM) were determined in vitro, adjusted for in vivo standards.  Husks had 55.6% DOM, leaf blades 40.7% and leaf sheaths 38.6%.  Husk and leaf CP was 3.75% and 5.75%, respectively.  Using in situ and mobile bag techniques, the rumen degradable protein (RDP) contents were 2.72 and 4.43% of DM, respectively.  Digestibility of the ruminally undegradable protein (RUP) was less than 25% for both husk and leaf.  Six to 10 plants are necessary to obtain representative results and residue energy values may be less than previously reported.

Keywords: corn residue, TDN, variation