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.

Production of comparatively wet pasture crop silages (>55% moisture) often occurs in response to uncooperative weather conditions, as farmers producing baled silages, rush baling operations to prevent damage to forage crops by impending rainfall events. Generally, wet silages are especially susceptible to secondary clostridial fermentations, producing butyric acid and ammonia as undesirable fermentation products, and susceptibility is enhanced further in baled compared to precision-chopped silages by the typically slower and less extensive fermentation characteristics of baled silages. In addition, baled silages can exhibit increased heterogeneity with respect to forage moisture compared to chopped silages; similarly, mixed-species baled silages can possess varying pockets of highly buffered forages, such as legumes (lucerne as example), further complicating fermentation. Another factor that potentially affects susceptibility of silages to secondary clostridial activity is the application of livestock manure onto the growing crop during the preceding growth cycle. The study of the authors cited endeavoured to investigate the effect of manure slurry further in addition to the effect of adding a microbial inoculant. Their objectives were to examine the inoculant as a mitigant of clostridial products in high-moisture, grass-legume (52% ± 13.8% cool-season grasses, 44% ± 14.0% legumes [predominantly Lucerne]) baled silages in swards that were fertilized with dairy slurry during the preceding growth cycle. A secondary objective was to examine the effects of bale moisture and inoculation on the aerobic stability of these silages following exposure to air

Treatments: 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 one week 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 results showed that total fermentation acids were affected by slurry application, but this was likely related to inconsistent bale moisture across slurry-application treatments. The concentrations of butyric acid were low, and there were no detectable contrasts comparing manure treatments. Bale moisture affected all measures of fermentation, with bales made at 64.1% moisture compared to 48.4% moisture exhibiting a more acidic final pH (4.39 vs. 4.63), less residual water-soluble carbohydrates (2.1% vs. 5.1%), as well as greater lactic acid (4.64% vs. 2.46%), acetic acid (2.26% vs. 1.32%), and total fermentation acids (7.37% vs. 3.97%). Inoculation reduced pH (4.47 vs. 4.56), and increased acetic acid (1.97% vs. 1.61%) and 1,2-propanediol (1.09% vs. 0.72%) compared to controls. During a 34-day aerobic exposure period, maximum surface bale temperatures were not affected by any aspect of treatment, likely due to the prevailing cool ambient temperatures; however, yeast counts were numerically lower in response to greater production of acetic acid that was stimulated by both high bale moisture and inoculation.

Discussion and implications of the results: Despite the application of dairy slurry, as well as greater-than-recommended bale moisture, only minimal concentrations of typical clostridial products were observed following fermentation. Inoculation had no effect on the final concentrations of either ammonia-N or butyric acid. The lack of clostridial response might be explained by numerous strong rainfall events during the growth of these forages, prompt wrapping following baling, substrate adequacy, as well as an exceptionally low buffering capacity, particularly compared to most mixed, grass-legume swards harvested previously at this location. As a result, using a combination hetero- and homolactic inoculant to mitigate clostridial activity was inconclusive. Both bale moisture and inoculation had positive effects on concentrations of acetic acid following fermentation, and resulted in numerically reduced counts of yeasts following a 34-day exposure to air. However, surface bale temperatures remained cool, regardless of treatment, largely in response to the cool ambient temperatures that occurred. This implies that the results could have been different if warmer weather, such as in the sub-tropics and tropics, occurred.