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.

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.