Case study: Fermentation profile, physical form, and starch digestibility of whole-plant corn silage harvested with novel processing

Abstract Text: Samples collected from two self-propelled harvesters (SPFH) at harvest were evaluated for fermentation profile, physical form, and ruminal in situ starch digestibility (StarchD; 12-h incubations on undried, unground samples) in whole-plant corn silage (WPCS). One SPFH was fitted with conventional type rolls with greater roll-speed differential than normal (CRGD). The other SPFH was fitted with intermeshing-disc type rolls (IMDR). The CRGD samples were from 3 theoretical lengths of cut (TLOC; 1.91, 2.24 and 2.54 cm; 3 mm roll-gap setting) on 2 hybrid types (leafy [LFY] and dual-purpose [DP]). The IMDR samples were from 3 TLOC (1.70, 1.91 and 2.54 cm) at 2 roll-gap settings (1.5 and 2.5 mm) on one hybrid. Unfermented samples were analyzed for processing score (CSPS) and mean particle length (MPL). Fermentation profile and StarchD were measured on fermented samples (30-d; vacuum-sealed bags). Data were analyzed using Proc Mixed of SAS with the Fixed effects of TLOC, hybrids and their interaction or TLOC, roll-gap settings and their interaction for CRGD and IMDR, respectively. For CRGD, CSPS tended (P < 0.06) to decrease while MPL increased (P < 0.001) with increasing TLOC. Fermentation profile and StarchD were unaffected (P > 0.10) by TLOC. Greater CSPS and reduced MPL were observed (P < 0.05) for LFY than DP. In addition, LFY had (P < 0.01) lower pH and greater total VFA concentrations. Starch digestibility tended (P < 0.10) to be greater for LFY than DP (79.9% vs. 71.2%). The difference in DM content between hybrids (P < 0.01; 31.2% vs. 35.2% for LFY and DP) may partially explain the differences between hybrid types. For IMDR, CSPS tended (P < 0.10) to be greatest for 1.70 cm TLOC. Greatest MPL was observed (P < 0.05) at the 2.54 cm TLOC. Measurements of pH were similar (P > 0.10) among TLOC, although total VFA concentration was lower (P < 0.01) for the 1.91 cm TLOC. A roll-gap set at 1.5 mm increased CSPS and decreased MPL compared to the 2.5 mm setting (P < 0.001). Total VFA concentration was similar (P > 0.10) and pH lower (P < 0.01) for the 2.5 mm treatment. Roll-gap and TLOC setting did not affect (P > 0.10) StarchD. Hybrid type and settings for TLOC and roll-gap influenced WPCS physical form and 30-d fermentation profile, while StarchD differed by hybrid type but not TLOC and roll-gap settings.

Keywords: corn silage, processing, starch digestibiity