Effects of stage of maturity and microbial inoculation at harvest on nutritive quality and degradability of grain sorghum whole-plant and head-chop silages

Grain sorghum silage is an attractive supplement for cattle grazing marginal areas where sorghum has agronomic advantages with respect to corn. The objective of this study was to evaluate a microbial inoculant as a management tool to improve the quality of whole-plant (WP) and head-chop (HC) grain sorghum silages. A completely randomized design with a 2x2 factorial arrangement of treatments was used in two experiments to evaluate effects of a commercial bacterial inoculant (Sil-All, Alltech Inc., Nicholasville, KY, USA) on DM recovery, OM degradation (OMD), fermentation, chemical composition and aerobic stability of WP ensiled at the milk stage (MS) of grain maturity and HC ensiled at the MS and dough stage (DS) of grain maturity. Both cultivars were ensiled with or without bacterial inoculant for 90d in triplicate mini-silos constructed from PVC pipe. Samples were collected before ensiling, after ensiling for 3 months (POST), and after exposing 3-month old silage to air for 3d (PAE). Samples were analyzed for pH, DM, CP, aNDF, WSC, NH₃-N and OMD after incubation with ruminal fluid for 72h. In Experiment 1, the ensiling process reduced the DM (P=0.007) and WSC (P=0.004) content and increased the aNDF (P=0.022) content of WP sorghum. Ensiling for 90d also increased the lag time (P=0.032) required for OM degradation of WP sorghum to begin. In Experiment 2, inoculation increased HC grain sorghum silage DM recovery over the control at MS (0.925 vs. 0.979, P=0.056 interaction between maturity at harvest and inoculation) but had no effect on DM recovery at the DS of maturity. Ensiling HC at MS resulted in lower (P<0.001) DM and WSC content, and higher (P<0.001) CP content than ensiling at DS. Microbial inoculation reduced (P=0.004) the rate of OMD in HC sorghum ensiled at the MS stage of grain maturity, and improved aerobic stability of HC sorghum silage regardless of grain maturity at harvest as indicated by lower (P<0.003) temperature after 3d for inoculated PAE silage. Microbial inoculation is most beneficial in HC sorghum silage ensiled at MS, but improves aerobic stability of sorghum silage regardless of maturity at harvest.