SO 2-treated straw as a silage additive: Fermentation data on lucerne with particular reference to protein degradation

Abstract

Untreated and sulfur dioxide-treated wheat straw (WS) were used as additives for ensiling low dry matter (DM) lucerne in laboratory silos. The negative control (L + WS) consisted of 60% lucerne + 40% untreated WS on a DM basis. SO 2-treated WS was added to the lucerne at 2 levels: 40% (L + 40% TWS) and 50% (L + 50% TWS) of the mixture DM. Lucerne wilted to reach the DM content of the above-mentioned mixtures (30%), was ensiled and served as the positive control (WL). Silos were opened after 90 days and the silages subjected to analyses. The highest DM loss (∼ 10%) was in the negative control (L + WS), whereas in the L + TWS silages DM loss was reduced to 0.5–4%. Lactic acid production was lower in the negative control (L + WS) because of the lack of fermentable sugars and in the L + 50% TWS because of the initial low pH of the mixture at ensiling (4.3). The greatest ability to preserve forage protein was found in the L + 50% TWS, in which nearly 80% of the protein was recovered after 90 days of fermentation, as compared with 43% in the L + WS and WL silages. Threonine and the basic amino acids were extensively degraded in the L + WS silages. The recovery of those amino acids was significantly higher in the L + TWS silages. Generally, the L + 50% TWS was the most successful treatment in preserving the forage amino acids. The concentration of phenylalanine was remarkably increased in silages which underwent extensive protein breakdown (L + WS and WL). In view of its ability to preserve energy and protein, SO 2-treated WS could be considered as a future silage additive for direct ensilage of high quality, low DM forages.