Influence of hexamine and sodium nitrite in combination with sodium benzoate and sodium propionate of fermentation and hygienic quality of wilted and long cut grass silage

Bale silage is usually made from long or restricted cut grass. Long cut herbage may be difficult to ensile, because of delayed and heterogenous fermentation. The aim of the present study was to find the optimal composition and level of an additive based on a mixture of hexamine, ie hexamethylene-tetraamine (HMTA) and sodium nitrite (NaN) together with sodium benzoate (NaB) and sodium propionate (NaP) to restrict aerobic deterioration. The silage crop (318 g DM kg-1; 158 g CP, 98 g ash, 89 g WSC, a buffering capacity of 200 mE and an ME value of 8.7 MJ per kg DM) consisting of about 30% ryegrass (Lolium perenne L), 30% meadow fescue (Festuca pratensis L) and 40% timothy (Phleum pratense L) was harvested by a self-loading wagon. Grass was ensiled in 41 PVC laboratory silos. Silos of each treatment were either closed immediately with a water-seal or aerated with 2.31 air per 24 h during the first 12 days of ensiling. Silages were treated with additives containing different concentrations and combinations of HMTA, NaN, NaB and NaP. Formic acid treated silage and untreated silage were used as controls. A mixture of HMTA and NaN (KSQ) improved fermentation by reducing pH, butyric acid, ammonia and increasing lactic acid and residual water-soluble carbohydrates (WSC) concentrations. This mixture also reduced the number of Clostridium spores in the silage. Addition to 300 g HMTA and 450 g NaN ton-1 FM was satisfactory to improve fermentation and restrict clostridial activity, but the aerobic stability of the silage was low. Addition of organic acid salts was more effective and improved both fermentation and storage stability. NaB (800 g) or a mixture of 690 g NaB and 210 g NaP was satisfactory to control aerobic stability. The use of HMTA and NaN in combination with NaB and NaP resulted in high hygienic quality and storage stability of silage made from unchopped and wilted grass.