Nutritive value, silage fermentation characteristics, and aerobic stability of grass-legume round-baled silages at differing moisture concentrations with and without manure fertilization and microbial inoculation

Abstract

For baled silages, production of clostridial fermentation products can be exacerbated by exceeding normal moisture targets (45% to 55%), and/or by the application of dairy slurry before harvest. Our objectives were to test a microbial inoculant as a mitigant of clostridial products in high-moisture, grass-legume (52% ± 13.8% cool-season grasses, 44.0% ± 14.0% legumes [predominately alfalfa]) baled silages in swards that were fertilized with dairy slurry. A secondary objective was to examine the effects of bale moisture and inoculation on the aerobic stability of these fermented silages following exposure to air. After the first-cutting was removed, three manure treatments were applied as a whole-plot factor: 1) control (no manure); 2) slurry applied immediately to stubble (63,250 L/ha); or 3) slurry applied after a 1-wk delay (57,484 L/ha). An interactive arrangement of bale moisture (64.1% or 48.4%) and inoculation (yes or no) served as a subplot term in the experiment. The inoculant contained both homolactic (Lactococcus lactis 0224) and heterolactic (Lactobacillus buchneri LB1819) bacteria. The experimental design was analyzed as a randomized complete block with four replications, and the study included 48 experimental units (1.2 × 1.2-m round bales). Total fermentation acids were affected (P ≤ 0.021) by slurry application strategies, but this was likely related to inconsistent bale moisture across slurry-Application treatments. Concentrations of butyric acid were low, and there were no detectable contrasts comparing manure treatments (mean = 0.05%; P ≥ 0.645). Bale moisture affected all measures of fermentation, with bales made at 64.1% moisture exhibiting a more acidic final pH (4.39 vs. 4.63; P < 0.001), less residual water-soluble carbohydrates (2.1% vs. 5.1%; P < 0.001), as well as greater lactic acid (4.64% vs. 2.46%; P < 0.001), acetic acid (2.26% vs. 1.32%; P < 0.001), and total fermentation acids (7.37% vs. 3.97%; P < 0.001). Inoculation also reduced pH (4.47 vs. 4.56; P = 0.029), and increased acetic acid (1.97% vs. 1.61%; P < 0.001) and 1,2-propanediol (1.09% vs. 0.72%; P < 0.001) compared to controls. During a 34-d aerobic exposure period, maximum surface bale temperatures were not affected (P ≥ 0.186) by any aspect of treatment, likely due to the prevailing cool ambient temperatures; however, yeast counts were numerically lower in response to greater (P < 0.001) production of acetic acid that was stimulated by both high bale moisture and inoculation.