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.

A study involving a 2 x 2 x 2 factorial arrangement of treatments was conducted to evaluate effects of hybrid (Pioneer 3335 and 3489), maturity (half milkline and blacklayer), and mechanical processing (field chopper with and without on-board rollers engaged) on intake and digestibility of corn silage. Forty Angus steers (322 +/- 5.2 kg BW) were assigned to the eight silage treatments (five steers per treatment) and individually fed using electronic gates. Diets consisted of 60% corn silage and 40% chopped alfalfa hay (DM basis). Following a 5-d adaptation period, intake was measured for 7 d and subsequently fecal samples were collected for 5 d. Chromic oxide (5 g/d) was fed beginning 7 d before fecal sample collection and digestibility was determined by the ratio of Cr in the feed and feces. Steers were reallocated to treatments and these procedures were repeated, providing 10 observations per treatment. In addition, all silages were ruminally incubated in six mature cows for 0, 8, 16, 24, 48, and 96 h to determine extent and rate of DM, starch, NDF, and ADF disappearance. Processing increased DMI of hybrid 3489 but did not affect DMI of hybrid 3335 (hybrid x processing; P < 0.06). Total tract digestibility of DM, starch, NDF, and ADF decreased (P < 0.01) as plant maturity increased. Maturity tended to decrease starch digestibility more for hybrid 3489 than for hybrid 3335 (hybrid x maturity; P < 0.10). Processing increased (P < 0.01) starch digestibility but decreased (P < 0.01) NDF and ADF digestibility, resulting in no processing effect on DM digestibility. There was a numerical trend for processing to increase starch digestibility more for latethan for early-maturity corn silage (maturity x processing; P = 0.11). Processing increased in situ rates of DM and starch disappearance and maturity decreased in situ disappearance rates of starch and fiber. These data indicate that hybrid, maturity, and processing all affect corn silage digestibility. Mechanical processing of corn silage increased starch digestibility, which may have been associated with the observed decreased fiber digestibility.

Two corn hybrids (Pioneer 3377 and 3389) with similar total plant and grain yield characteristics were evaluated to determine potential differences in nutritive value of the whole plant and stover. Hybrids were grown in plots at four different locations in Idaho in 1988 and 1989 for laboratory evaluation. Samples from the plots were stored fresh or ensiled with or without a microbial inoculant for 60 d in laboratory silos. Whole-plant samples of 3377 had a lower (P < .01) percentage of NDF (42.7 vs 48.1), ADF (26.3 vs 30), hemicellulose (16.2 vs 18.2), cellulose (21.4 vs 24), and lignin (3.4 vs 3.8). Similar differences, but of larger magnitude, were observed in stover samples. Ruminal in situ (24 h) and two-stage IVDMD of whole-plant and stover samples were greater (P < .01) for 3377 than for 3389. Lower fiber content and greater degradability for 3377 was not due to greater grain content; 3377 actually had numerically lower grain as a percentage of whole plant than 3389 (41 vs 44). Ensiling reduced (P < .05) NDF, hemicellulose, and cellulose content compared with fresh samples; however, no effect (P > .10) due to inoculant was noted. Hybrid x storage interactions were not observed (P > .10). Inoculation and hybrid did not affect (P > .10) organic acid concentration of the silages. In 1989 silages from 3377 and 3389 were harvested to evaluate diets containing 65% (DM basis) corn silage in steer digestion and growth trials.(ABSTRACT TRUNCATED AT 250 WORDS)

This research was conducted to determine the effect of corn genetics and cutting height on the composition and nutritive characteristics of corn silage. An in situ study involving eight commercially available corn hybrids indicated main effects and interactions (P < 0.01) of hybrid and cutting height on NDF, ADF, and starch content and on in situ DM and NDF degradablility. Four ruminally cannulated Angus heifers (initial BW = 378 +/- 3 kg) were used in a 4 x 4 Latin square digestion experiment with a 2 x 2 factorial treatment arrangement. Main effects and interactions of hybrid (Pioneer Hi-Bred Int., Inc., hybrids 3335 and 3223) and cutting height (LO = 20.3 cm, and HI = 61 cm) were evaluated. Dietary treatment consisted of 40% chopped alfalfa hay and 60% corn silage. Although corn silage hybrids used were of equivalent maturity at harvest (60% milkline), 3335 treatments had 37.8% starch and 34.8% NDF, whereas 3223 treatments had 33.7% starch and 38.6% NDF. The LO treatments averaged 3.1 percentage units greater in NDF and 3.45 percentage units less in starch content than the HI treatments. Intake of DM was greater for heifers fed 3335-HI than 3335-LO; however, DMI was greater by heifers fed 3223-LO than 3223-HI (hybrid x cutting height interaction, P < 0.05). Starch intake was greater (P < 0.05) and NDF intake was less (P < 0.05) by heifers fed HI vs. LO and fed 3335 vs. 3223 dietary treatments. Digestibility of DM, starch, and NDF was greater (P < 0.05) by heifers fed 3223 than 3335 dietary treatments, but digestibility differences were not observed (P > 0.10) between cutting heights. Rate of in situ DM and starch degradability was not affected (P > 0.10) by hybrid or cutting height; however DM degradability was greater (P < 0.05) for HI than LO corn silage substrates at 8, 16, and 24 h of incubation. Rate of NDF degradability tended (P = 0.08) to be greater for 3223 than for 3335, and for LO compared with HI corn silage. Degradability of NDF was greater (P < 0.05) for 3223 compared with 3335 substrates at 24, 36, and 48 h of incubation. These data suggest fiber may not be an accurate measure of corn silage quality. Whereas cutting height affected chemical composition, we observed genetics to have a greater effect on corn silage quality.

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