Storage characteristics, nutritive value, and fermentation characteristics of large, round bales of alfalfa-mixed grass forage wrapped with different layers of stretch film1

Baled silage has become a popular form of forage conservation; however, many practical management questions have not been investigated thoroughly. Our objectives were to evaluate the number of polyethylene wrapping layers and the presence (OB) or absence (SUN) of an O2-limiting barrier within the wrap on the storage characteristics, nutritive value, and silage fermentation characteristics of alfalfa-mixed grass round-bale silages. Thirty-six 1.2 × 1.2-m large, round bales of a mixed sward composed predominantly of alfalfa (Medicago sativa L.; 82 ± 3.8% alfalfa, DM basis) were packaged at 59.8 ± 3.2% DM and wrapped the same day with 4, 5, or 6 layers of the 2 polyethylene films (OB or SUN). Bales were sampled after 127 d at 0 to 0.15-m (SURFACE) and 0.15 to 0.61-m (CORE) depths. Generally, plastic type and number of wrapping layers had minimal effect on nutritive value and silage fermentation characteristics. However, greater concentrations of total fermentation acids, lactic acid, and NH3-N were found within the SURFACE compared with CORE layer (P ≤ 0.03), but the titratable acidity (mean = 15.4 mEq/kg of DM; P = 0.27) and final pH (mean = 5.70; P = 0.23) did not differ. Although yeast and mold counts at the SURFACE layer often were nondetectable (<3.0 log10 cfu/g), elevated counts were most frequently associated with SUN. An O2-limiting barrier may improve anaerobic integrity at the surface layer of baled silages, but the potential to reduce polyethylene usage may be limited by the risk of internal physical puncture by coarse alfalfa stems.