– K. Coblentz, R. K. Ogden, M. S. Akins, and E. A. Chow, originally published in its entirety in The Professional Animal Scientist 32 (2016):777–783 and condensed here by Steve Boyles, OSU Beef Extension Specialist
Production of baled silage is an alternative for livestock producers in part because it reduces risks of rain damage to wilting forage crops. However, silage fermentation within wrapped round bales differs from conventional chopped silages because the forage is considerably drier (45to 55% dry matter) than conventional chopped alfalfa silages (≥30% dry matter). This restricts production of fermentation acids and limits the associated pH depression within the silage. Furthermore, the long-stem nature of baled forages restricts the release of sugars required for fermentation by lactic acid–producing bacteria. This slows the rate and limits the extent of silage fermentation.
Exclusion of oxygen becomes very critical in the preservation of balege silages. One study published in 2006, evaluated the number of polyethylene wrapping layers on the subsequent preservation of alfalfa baled silage and determined that 2 layers was inadequate for preservation, but there was little advantage gained by using more than 4 film layers within a 5-mo storage period. Similar observations were made in a 2009 with perennial ryegrass in Ireland.
Although 4 polyethylene layers may permit acceptable fermentation, practical field observations suggest this standard of plastic usage is somewhat precarious, and may be unacceptable to many producers for physical reasons, such as the risk of internal puncture by alfalfa stems during handling. The objectives of this present study were to test the effects of 4, 5, or 6 layers of plastic wrap on the silage fermentation, storage characteristics, and the nutritive value of baled alfalfa–mixed grass silages. Another objective was to evaluate a prototype bale wrap containing an oxygen-limiting barrier against the identical polyethylene wrap without the oxygen-limiting barrier.
Thirty-six large round bales composed predominantly of alfalfa were packaged at about 60% dry matter and wrapped the same day with 4, 5, or 6 layers of the 2 types polyethylene wraps. Bales were sampled after 127 days on the surface of the bale (0 to 6 inches) and to the core (6 to 24 inches).
Generally, alfalfa–mixed grass, round-bale silages packaged at relatively high dry matter (59.8%) were adequately preserved by polyethylene wraps applied in 4, 5, or 6 layers, either with or without an oxygen barrier inserted into the wrap. Only minor differences in fermentation and nutritive value were observed in response to treatment. Mold and yeast counts should be responsive to oxygen permeability, but were frequently nondetectable. Detectable counts occurred more frequently, and were substantially greater in magnitude, without the oxygen barrier. However, bale numbers were inadequate to draw conclusive statistical inference. Based on visual observation, the threat of internal puncture by coarse alfalfa stems probably establishes a minimum threshold of 4 polyethylene layers for acceptable storage. The concept of an oxygen barrier may be viable, but the potential to reduce polyethylene use may be limited by potential for physical puncture as wrapping layers are reduced.