Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/17/2017
Publication Date: 6/15/2017
Citation: Coblentz, W.K., Ogden, R.K., Akins, M.S., Chow, E.A. 2017. Nutritive value and fermentation characteristics of alfalfa-mixed grass forage wrapped with minimal stretch film layers and stored for different lengths of time. Journal of Dairy Science. 100:5293-5304. Interpretive Summary: A key aspect of managing baled silages is to quickly achieve, and then rigorously maintain, anaerobic conditions within the silage mass. Recently, the concept of inserting an oxygen-limiting barrier into commercial silage plastic wraps has been evaluated, yielding mixed and/or inconclusive results. Our objective for this study was to maximize the challenge to a commercial polyethylene bale wrap, or the identical wrap containing an oxygen-limiting barrier, by using minimal plastic (4 layers) and then extending storage periods for as long as 357 days. An additional challenge to the integrity of the plastic was created by baling alfalfa-mixed grass forage at an ideal moisture for baled silage (47.5%), or at a much drier moisture concentration (36.1%). Overall, the quality of the silage was primarily influenced by bale moisture, with the silage baled at the ideal moisture being of better quality. From a nutritive standpoint, the loss of nutrients due to the ensiling process was modest and similar across all bales within this study. Insertion of an oxygen-limiting barrier into the plastic wrap had little effect on silage fermentation or post-ensiled nutritive value compared to a commercial plastic wrap managed in an identical manner. It remains unclear when, or under what conditions, the concept (and additional cost) of an oxygen-limiting bale wrap can be justified.
Technical Abstract: A key aspect of managing baled silages is to quickly achieve, and then rigorously maintain anaerobic conditions within the silage mass. Recently, the concept of inserting an O2-limiting barrier (OB) into plastic commercial silage wraps has been evaluated in some studies, yielding mixed and/or inconclusive results. Our objective for this study was to maximize the challenge to a commercial polyethylene bale wrap, or the identical wrap containing an OB, by using minimal plastic (4 layers), and then extending storage periods as long as 357 d. Forty-eight 1.2 × 1.2-m large-round bales of alfalfa (Medicago sativa L.)/mixed grass forage (66.3 ± 8.66% alfalfa; DM basis) were made at 2 moisture concentrations [47.5 (IDEAL) or 36.1% (DRY)], wrapped with 4 layers of plastic containing an OB or no OB (SUN), and then stored for 99, 243, or 357 d. After storage, yeast counts within the 0.15-m deep surface layer were not affected by any aspect of treatment (¯X = 5.85 log10 cfu/g; P = 0.072); mold counts could not be analyzed statistically because 26 bales were non-detectable at a 3.00 log10 cfu/g detection limit, but means among detectable counts were numerically similar for OB (4.74 log10 cfu/g) and SUN (4.77 log10 cfu/g). Fermentation characteristics were most affected by initial bale moisture, resulting in a more acidic final pH for IDEAL compared to DRY bales (5.52 vs. 6.00; P < 0.001). This was facilitated by greater concentrations of total fermentation acids (3.80 vs. 1.45% of DM; P < 0.001), lactic acid (2.24 vs. 0.71% of DM; P < 0.001), and acetic acid (1.07 vs. 0.64% of DM; P < 0.001) within IDEAL compared to DRY silages. Plastic wrap type had no effect on final concentrations of any fermentation product (P = 0.209). During fermentation and storage, there was greater change (P = 0.049) in concentrations of fiber components and whole-plant ash within the 0.15-m deep surface layer than in the bale core, and these changes always differed statistically (P < 0.01) from 0 (no change) based on pre-ensiled baseline concentrations. Overall, concentrations of water-soluble carbohydrates were reduced (¯X = 2.3 percentage units) during fermentation and storage, which resulted (indirectly) in increased concentrations of fiber components and CP, as well as an overall energy cost of 2.2 percentage units of TDN. It remains unclear under what conditions an OB plastic wrap will consistently benefit the fermentation and preservation of baled silages.