Effect of additives on the fermentation profile, microbial colonization and oxygen stress of alfalfa silages

Alfalfa is a popular source of proteins in diets for ruminants even though the plant is difficult to ensile. The high content of crude protein, high buffering capacity, low concentration of soluble carbohydrates, an undesirable content of nitrate(V) and the presence of epiphytic lactic acid bacteria justify the use of biological or chemical additives when ensiling this raw material. The study was performed to assess the effectiveness of an inoculant and a combined additive (microbiological preparation and potassium sorbate) for alfalfa ensilaging. Wilted green forage was ensiled in 12 mini-silos and stored for 12 weeks. Three variants of silages were prepared: control with no additive and test variants with inoculant and combined additives. The following were determined in the collected samples: chemical composition (green forage and silages), counts of lactic acid bacteria, aerobic mesophilic bacteria, yeasts and moulds (green forage and silages), the level of toxins − aflatoxins, ochratoxin A, toxins T-2 and HT-2, nivalenol, deoxynivalenol, zearalenone (green forage and silages), the quality of silages (pH value, content of alcohol and volatile fatty acids, aerobic stability). The additives clearly have improved the fermentation profile but have not increased the oxygen stability of silages. The highest efficiency was determined for the combined additive, which significantly decreased the pH value, increased the content of lactic acid and acetic acid, reduced the count of aerobic mesophilic bacteria and slightly decreased the count of moulds in relation to the control silage or silage with the inoculant. The only moulds detected silage with the combined additive belonged to Penicillium, but the silage with the inoculant contained Mucorales beside Penicillium. The effect of the combined additive containing a microbiological preparation and potassium sorbate on ensiling alfalfa was stronger than that produced by the inoculant.