Aerobic stability of native tropical grasses and grain sorghum silage stored at different temperatures
In two experiments the effect of storage temperature on aerobic stability of silages of native tropical grasses (NTG) treated with a lactic acid-producing bacterial inoculant and of grain sorghum was evaluated. In Exp. 1, NTG were harvested at 30% DM, chopped, and packed into PVC lab scale micro-silos (1.8 kg net). Ensiled material was stored at room (RT, 28-30ºC) or controlled (CT, 20-22ºC) temperature and assigned to one of four treatments: no additive at RT, inoculant at RT, no additive at CT, and inoculant at CT. Three silos per treatment were prepared and analyzed for initial pH. Silage mass temperature was monitored daily during the fermentation period (30 d). Silage from the opened silos was exposed to aerobic conditions for 3 d and analyzed for pH, in vitro dry matter degradability (IVDMD) and dry matter recovery (DMR). Final pH and silage mass temperature during the entire fermentation period were lower (P<.01) in NTG stored at CT than at RT. However, pH, IVDMD, and DMR were similar (P>.05) for all treatments after 3 d of aerobic exposure, regardless of addition of the bacterial inoculant. In Exp. 2, second cutting grain sorghum (28.25 DM%) was harvested at 75 d of growth, chopped and packed into micro-silos, twelve of which were stored at RT and 12 at CT (as above) during the fermentation process (FP). After 60 d of ensiling, three silos from each temperature were opened and silage exposed to aerobic conditions for 3 d at the same FP temperature. The other six silos were exposed to air at the temperature inverse to that of the FP. Silage exposed to air at CT had lower (P<.01) pH and higher (P<.01) IVDMD and DMR than that exposed at RT during the entire aerobic exposure period. After 1 and 3 d of aerobic exposure, temperature was lower (P<.01) in silage at CT than in that at RT. These results demonstrate the detrimental effect of high storage temperature on the aerobic stability of NTG and grain sorghum silage.