The nutritive value of corn (Zea mays L.) grain remains relatively constant; nutrient content and digestibility, however, may vary significantly in the remaining corn plant parts. Understanding of the relationships between plant maturity and plant component yield, nutrient content, and digestibility is important for prudent harvest management of nongrain corn parts. Six corn hybrids planted at two locations (Nampa, ID, and Modesto, CA) were used to evaluate the effects of maturity on yield, chemical composition, and ruminal fermentability of whole plant, ear, and stover. Maturities evaluated were: A, milk line ⅓ from the top of the kernel; B, milk line ⅔ from the top of the kernel; and C, black layer formation. Location × maturity interactions were not observed, therefore data were pooled across location. Neutral and acid detergent fiber (NDF and ADF) increased (P < 0.01) in stover and decreased (P < 0.05) in whole plant and ear samples when maturity advanced from A to B. Stover samples showed a further increase (P < 0.01) in these fiber components as maturity advanced from the B to the C stage. Whole plant and ear fiber composition did not change (P > 0.10) between the B and C maturities despite a progressive increase (P < 0.01) in grain composition of the whole plant. Calculations of total digestible nutrients (TDN) and net energy for lactation (NE1) based on the ADF content of the samples indicated differences (P < 0.01) between B and C maturities for stover samples but not for whole plant and ear samples. Stover samples, but not whole plant and ear samples, increased (P < 0.05) in lignin content with each increase in maturity. When ruminal fermentability was measured by incubating samples in situ for 24 h, percent dry matter (DM) disappearance was reduced (P < 0.01) with each advance in maturity for both the stover and the whole plant samples. The lower in situ DM disappearance for C vs. B maturity whole plant samples, which was not reflected in a similar reduction in calculated TDN, suggests an inadequacy in using ADF content as the sole indicator of the whole plant energy value. Yield of DM and of calculated TDN reached a plateau at the B maturity as no differences were observed for B vs. C maturity. These data indicate benefits to harvesting at proper maturity stages for corn whole plant, ear and especially stover.
Total dry matter (DM) yield and grain content are commonly considered the most important factors forevaluating corn (Zea mays L.) hybrids for silage production with no considerationgiven to the nutritive value of the nongrain portion of the plant. Because the nongrain portion mayrepresent over 50% of the total DM in corn silage, we hypothesized that hybrid differences inchemical composition and ruminai fermentability of the stover portion of the plant may account forimportant nutritional differences in corn hybrids. Six corn hybrids were planted at two locations(Nampa, ID, and Modesto, CA) and were harvested at three stages of plant maturity. Differences (P <0.01) in content of fiber components in whole plant and stover were observed amonghybrids. Ranges in hybrid means for whole plant and stover samples were: neutral detergent fiber(NDF), 41.7 to 49.0 and 50.3 to 64.1%; acid detergent fiber (ADF), 23.9 to 28.3 and 31.7 to 41.0%;cellulose, 19.2 to 22.6 and 25.5 to 33.1%; and lignin, 2.6 to 3.3 and 3.1 to 4.4%, respectively.Hybrid composition differences in total sugar and starch of stover and total sugar of whole plantalso were observed. In situ DM degradability after 24 h of ruminai incubation ranged among hybridsfrom 53.7 to 60.6% for whole‐plant samples and from 44.0 to 52.3% for stover samples. Importantly,those hybrids with lower fiber content or higher in situ fermentability did not necessarily havegreater proportion of grain in the whole plant, suggesting that selection of high quality silagehybrids may be accomplished by selecting for both high stover digestibility and high grain yields.Correlation coefficients for whole‐plant in situ DM degradability with neutral detergent fiber, aciddetergent fiber, cellulose, lignin, and starch were −0.85, −0.80, −0.79, −0.58, and 0.69,respectively. Results of this study indicate that differences among corn hybrids in whole‐plant andstover fiber content may be important in identification of hybrids with improved silage feedingvalue.
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