Effects of low temperature and ensiling time on fermentation and nutritive value of sorghum- sudangrass silage

Abstract

Objective

The study evaluated the fermentation and nutritive value of freeze-affected sorghum-sudangrass si- lage stored at 2 temperatures.

Materials and Methods

Sorghum-sudangrass for- age affected by several frost/freeze events and lodging was harvested and chopped, then ensiled in vacuum-sealed plastic mini-silos. Silos were stored at either 4°C or 20°C for 5, 10, 15, 30, or 60 d with triplicate silos at each time. Resulting silage was evaluated for pH, silage acids and al- cohols, nitrates, and nutritive value. Aerobic stability was also measured on silages stored for 60 d.

Results and Discussion

Silage pH decreased more quickly at 20°C, with silage at 4°C having a 10-d lag be- fore pH decreased. Lactic, acetic, and propionic acid con- centrations were greater at all times for silage stored at 20°C. Ethanol and methanol were greater in silage stored at 20°C, which is speculated to be from increased yeast activity. The decreased fermentation for silage stored at 4°C resulted in 1% greater DM recovery; however, aerobic stability was better for silage stored at 20°C (149 h) than 4°C (47 h) likely due to greater acetic acid concentration. Silage storage at 4°C resulted in lower NDF concentration due to less silage acid production, with no other changes in nutritive value observed due to storage temperature. Nitrate concentrations were low in the initial forage (76 mg/kg DM) with concentrations lower after storage (43– 50 mg/kg DM), as expected.

Implications and Applications

Storage temperature of sorghum-sudangrass silage had a significant impact on silage acid production and aerobic stability with limited fermentation the first 10 to 15 d of storage. This research is applicable when harvesting forage during cold or freez- ing temperatures, which limits early fermentation. Allow- ing standing forage to thaw/warm before harvest may improve fermentation and aerobic stability. Additional research on changes in nitrates of frosted sorghum forage is needed to confirm results in forage with high initial nitrate levels.