The effect of harvest date and additives on chemical composition and aerobic stability of sorghum silage

Abstract

The objective of the experiment was to determine the effect of harvest date of sweet sorghum forage and the addition of bacterial, bacterial-chemical or chemical additives on chemical composition, fermentation quality and aerobic stability of the silages obtained. Sweet sorghum (Sorghum saccharatum, cv. Sucrosorgo 506) forage mown at two dates (E – 28 September 2008 and L – 13 October 2008) was ensiled in 120 L experimental silos. Forage from each harvest date was ensiled without (E-UT, L-UT) or with the addition of Lactobacillus buchneri (5.0×105 cfu·g-1 of forage) – E-LB, L-LB; L. buchneri (5.0×105 cfu·g-1of forage) with potassium sorbate (0.3 g·kg-1 of forage) – E-LBS, L-LBS; propionic acid, formic acid and ammonium propionate (3 ml·kg-1 of forage) – E-PFA, L-PFA. Both, forage harvest date and applied additives had a significant effect (P<0.001) on dry matter (DM), crude protein (CP) and true protein (TP), water-soluble carbohydrates (WSC), neutral-detergent fibre (NDF), acid-detergent fibre (ADF) and the starch content in silages. All the additives limited the degradation of protein to ammonia. The additives prevented butyric fermentation and limited (P<0.001) alcoholic fermentation in the silages. Forage harvest date itself had no influence on the silage aerobic stability. However, significant interaction between the effect of harvest date and additives was found. The duration of aerobic stability was 36-41 h for untreated silages, 84-88 h for silages with L. buchneri, 95-99 h for silages with L. buchneri and potassium sorbate, and 66-68 h for silages with the chemical preservative.