Silage review: Interpretation of chemical, microbial, and organoleptic components of silages

Ensiling is a method of preserving a moist crop. A moist crop can support the growth of a wide range of microorganisms, most of which will degrade the nutrient value to livestock. However, ensiling generally controls microbial activity by a combination of an anaerobic environment and a natural fermentation of sugars by lactic acid bacteria on the crop. This fermentation and the resulting low pH primarily suppress the growth of other anaerobic microorganisms. The fermentation can also inhibit yeasts, molds and aerobic bacteria, but the anaerobic environment is essential to preventing most of the spoilage microorganisms from growing. Inoculants have become the dominant additives for making silage. Homofermentative strains help guarantee a rapid suppression of anaerobic stains early in storage, increase dry matter recovery and have improved animal performance by means that we do not fully understand. Inoculants containing Lactobacillus buchneri, a heterofermentative species capable of fermenting lactic acid to acetic, are recent additives. The added acetic acid inhibits yeast and mold growth, increasing aerobic stability of silages at feeding.

Several microorganisms and one chemical preservative were tested for their effects on the fermentation and aerobic stability of corn silage. Whole-plant corn (one-half milk line, 31.3% dry matter) was ensiled in quadruplicate 20-L laboratory silos untreated or after the following treatments: Lactobacillus buchneri at 1 x 10(5) and 1 x 10(6) cfu/g of fresh forage; two different strains of L. plantarum, each at 1 x 10(6) cfu/g; and a buffered propionic acid-based product at 0.1% of fresh forage weight. After 100 d of ensiling, silage treated with L. buchneri (1 x 10(6) cfu/g) had a lower concentration of lactic acid compared with the untreated silage, but was similar to other treated silages. The silage treated with the high (1 x 10(6) cfu/g), but not the moderate rate (1 x 10(5) cfu/g) of L. buchneri also had a greater concentration of acetic acid (3.60%) and less yeasts (2.01 log cfu/g) when compared with other treatments (average of 1.88% acetic acid and 5.85 log cfu of yeasts/g). Silages treated with L. plantarums, the moderate rate of L. buchneri, and the chemical preservative took longer to heat than untreated silage when exposed to air, but improvements were numerically small (6.3 to 10.5 h). In contrast, silage treated with the high rate of L. buchneri never heated throughout a 900-h period of monitoring. Inoculating corn silage with 1 x 10(6) cfu/g of L. buchneri resulted in a more heterolactic fermentation and dramatically improved the aerobic stability of corn silage.