Nutritive value, silage fermentation characteristics, and aerobic stability of round-baled, alfalfa–grass forages ensiled at 2 moisture concentrations with or without a propionic-acid-based preservative*

Abstract

Objective: Propionic-acid-based products are used commonly for storage of dry hay but are not often considered when ensiling baled forages. The objectives for this study were to test several application rates of a propionic-acid-based preservative on the storage efficiency, nutrient preservation, fermentation characteristics, and aerobic stability of alfalfa–grass silages. Materials and Methods: This study evaluated 4 preservative treatments applied to alfalfa–grass forages that had received 5.1 mm of unexpected rainfall during wilting. A propionic-acid-based preservative was applied at rates of 0.01 (control), 0.13, 0.44, or 0.80% of wet bale weight to 24 (1.2 × 1.2 m) round bales made at either 43.6 or 51.6% moisture. Aerobic stability was then evaluated by removing plastic film from all bales and monitoring surface bale temperatures for 11 d during spring. After exposure, surface and core samples were evaluated further for residual fermentation products and pH. Results and Discussion: Before fermentation, forage pH declined linearly (P < 0.001) from 6.14 to 5.77 with increasing product-application rates. After 242 d of storage, there were linear increases in concentrations of total alcohols (P = 0.002), and particularly 2,3-butanediol (P < 0.001), with increasing preservative application rates. After aerobic exposure, maximum surface temperatures (0.15-m depth) declined linearly (P = 0.001) from 55.6 to 17.9°C with preservative application rate. A similar linear (P = 0.002) effect was observed for exposed surface pH (range = 6.52 to 5.41). Implications and Applications: Propionic-acid-based preservatives improved aerobic stability of round-bale silages, but the additional cost must be a critical component of any overall management strategy.