Effect of ensiling time on fermentation profile and starch digestibility in whole plant corn silage from two different hybrid types

Abstract Text: The objective of this study was to evaluate the effect of ensiling time and hybrid type on fermentation profile, soluble CP (% CP), ammonia-N (% N) and ruminal in vitro starch digestibility (ivStarchD; 7 h incubations on dried and 6 mm ground samples) in whole plant corn silage (WPCS). Samples from 8 hybrids (4 leafy [LFY] and 4 brown midrib [BMR]; Mycogen Seeds, Dow AgroSciences LLC, Indianapolis, IN) were collected at harvest, vacuum-sealed in plastic bags and ensiled for 0, 30, 120 and 240 d. Samples were stored at room temperature in the dark and immediately frozen to stop the fermentation until processed for analysis. Samples were analyzed for fermentation profile, CP, soluble CP, ammonia-N, starch and ivStarchD at Dairyland Laboratories Inc. (Arcadia, WI). Data were analyzed using Proc Mixed of SAS with the Fixed effects of ensiling time, hybrid type and their interaction. Regressions to determine linear relationships between ivStarchD and ammonia-N and soluble CP contents were performed using Proc Reg in SAS. Contents of DM and starch (DM basis) were unaffected (P > 0.10) by ensiling time or hybrid type and averaged 39.3% and 40.0%, respectively. Fermentation profile, ammonia-N, soluble CP and StarchD were similar (P > 0.10) between hybrid types. Measurements of pH did not differ (P > 0.10) even though lactate, acetate and total VFA concentrations were greater (P < 0.01) for WPCS fermented for 30, 120 and 240 d compared to unfermented samples. Gradual increases were observed (P < 0.001) from 0 to 240 d for Soluble CP (33.5, 41.2, 48.9 and 54.5% of CP for 0, 30, 120 and 240 d, respectively) and ammonia-N (2.6, 4.6, 6.0, and 7.9% of N for 0, 30, 120 and 240 d, respectively). Likewise, the ivStarchD measurements increased with ensiling time (P < 0.001; 50.2, 58.5, 65.8, 71.4% of starch for 0, 30, 120 and 240 d, respectively). Positive relationships between ivStarchD and ammonia-N (R² = 0.67; P = 0.001) and soluble-CP (R² = 0.55; P = 0.001) were observed. Fermentation profile, ammonia-N, soluble CP and ivStarchD were influenced by ensiling time but not hybrid type. Ammonia-N and soluble CP were both good indicators of ivStarchD in WPCS.

Keywords: corn silage, ensiling time, starch digestibility