Influence of plant population, maturity and ensiling time on fermentation profile, nitrogen fractions and starch digestibility in earlage

Abstract Text: The objective of this study was to evaluate the effect of  plant population, maturity at harvest, and ensiling time on fermentation profile, N fractions and ruminal in vitro starch digestibility (ivSD; 7 h incubations on dried and 4 mm ground samples) in earlage (contains husks, kernels, and cob). Samples from 4 hybrids (used as experimental unit), each planted at 4 different plant populations (64,000 [64K], 79,000 [79K], 94,000 [94K] or 109,000 [109K] plants/hectare) and harvested at 2 maturities (1/2 kernel milk line [1/2ML] or black layer [BL]), were collected at harvest, inoculated (Buchneri 500; Lallemand Animal Nutrition, Milkwaukee, WI) and ensiled in vacuum-sealed bags for 30, 60, 120 and 240 d. Ensiled and fresh samples were analyzed at Dairyland Laboratories Inc. (Arcadia, WI). Data were analyzed using Proc Mixed of SAS with the Fixed effects of ensiling time, plant population, maturity and their interactions. Regressions to determine linear relationships were performed using Proc Reg in SAS. Except for greater (P = 0.01) DM content for 64K than 94K and 109K or slightly greater ivSD for 94K than other treatments (P = 0.04; 65.5% vs. 63.3% of starch, on average), no effects of plant population were observed (P > 0.10). Although contents of DM, CP, starch and sugars were greater (P > 0.01), lactate, acetate, 1,2-propanediol, ethanol and total acid concentrations were lower, and thus pH was greater, in BL earlage. Furthermore, soluble CP and ammonia-N concentrations, and ivSD were reduced by 5.5, 1.0 and 8.3%-units, respectively, in BL than 1/2ML. Measurements of pH were greater (P = 0.001) for 30 d than the other ensiling times in relationship to a shift in fermentation from lactate (P = 0.001) towards acetate and 1,2-propanediol (P = 0.001) as fermentation progressed. Gradual increases were observed (P < 0.001) from 30 to 240 d for soluble CP (40.6, 47.6, 49.7 and 69.5% of CP) and ammonia-N (4.3, 5.4, 5.9, and 9.6% of N). Likewise, the ivSD measurements increased with ensiling time (P < 0.001; 57.9, 59.9, 67.8, 69.9% of starch). Both, ammonia-N (R² = 0.42; P = 0.001) and soluble-CP (R² = 0.45; P = 0.001) were positively related to ivSD. Fermentation profile, N fractions and ivSD of earlage were influenced to a greater extent by ensiling time and maturity than plant populations. Ammonia-N and soluble CP were both good indicators of ivSD in earlage.

Keywords: earlage, ensiling time, starch digestibility