Storage characteristics and nutritive value of moist large-round bales of alfalfa or alfalfa-grass hay treated with a propionic-acid-based preservative

Authors: Coblentz, Wayne; AKINS, MATTHEW - University Of Wisconsin; KIEKE, BURNEY - Marshfield Clinic Research

Submitted to: Applied Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2020
Publication Date: 7/25/2020
Citation: Coblentz, W.K., Akins, M.S., Kieke, B.A. 2020. Storage characteristics and nutritive value of moist large-round bales of alfalfa or alfalfa-grass hay treated with a propionic-acid-based preservative. Applied Animal Science. 36:455-470. https://doi.org/10.15232/aas.2020-02024.
DOI: https://doi.org/10.15232/aas.2020-02024

Interpretive Summary: Past studies have shown inconsistent benefits from applying propionic-acid-based preservatives to alfalfa hays. Two studies were conducted to evaluate the effects of bale diameter and acid-application strategies on heating characteristics, recovery of dry matter, and nutrient retention during storage. Although these studies do not completely explain the factors complicating the successful use of propionic-acid-based preservatives, two key findings are important: i) based on the greater heating responses for 1.5- compared to 1.2-m-diameter round bales, it is likely that bale size greatly affects product effectiveness; and ii) when preservative application does not effectively control spontaneous heating, internal bale temperatures within treated hays will exhibit a secondary heating response, usually modest in magnitude, that may persist for months after baling. Furthermore, this work suggests that recommended application rates for these products may be overly simplistic, and that a complex array of factors, such as bale type, bale size and/or weight, bale density, bale moisture, predominant moisture type (stem or dew), and inside or outside storage should be considered in any adjustment of application-rate recommendations.

Technical Abstract: Spontaneous heating in dry hays is exacerbated by the increased size of large hay packages commonly used today. Our objectives for 2 experiments were to evaluate a propionic-acid-based preservative applied to large-round bales of alfalfa or alfalfa/grass hay with a HarvestTec 647C Applicator. In Experiment 1, 18 large-round bales (83% alfalfa, 17% mixed grass) were baled at 20.6% moisture with a 2 × 3 factorial arrangement of bale diameters (1.2 or 1.5 m) and preservative application strategies [fully automated with adjustments for bale moisture and baling rate, fully automated assuming a constant baling rate, or control (no preservative)]. All measures of spontaneous heating differed between 1.2- and 1.5-m bale diameters with the larger diameter exhibiting greater maximum internal bale temperatures (46.1 vs. 41.6oC) and greater total heating degree days > 30oC (HDD) incurred during storage (334 vs. 106 HDD). However, acid-treated bales collectively exhibited less heating than control hays only for the mean internal bale temperature during the first 30 d of storage (32.0 vs. 38.3oC). The 2 preservative-application methods did not differ for any measure of heating, and DM recoveries were not affected by treatment. For Experiment 2, 28 large-round bales of alfalfa hay were produced at 20.2% moisture; 16 bales were made with fully-automated preservative application and 12 bales were untreated controls. Although all acid-treated hays exhibited temperature suppression during the first 25 d of storage, 9 bales receiving the preservative continued to accumulate HDD throughout the entire storage period, while 7 bales did not. These divergent heating responses yielded a difference in total accumulated HDD (616 vs. 236 HDD), where those continuing to accumulate HDD throughout the study did not differ from control hays (628 HDD). However, both groupings of acid-treated hays tended to or recovered greater percentages of DM than control bales (95.5 or 95.6 vs. 93.7%). Changes in energy density (TDN) were closely associated with heating characteristics; the greatest losses were observed in control bales (4.5 units), which differed from acid-treated hays in which heating was controlled (3.4 units). Bale size has a strong effect on preservative effectiveness, and the secondary and extended heating response exhibited by some acid-treated hays partially explains the mixed overall responses to preservative application noted in some previous experiments.