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 potentially inadequate for large hay packages, 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: Objectives: Our objectives for 2 experiments were to evaluate storage characteristics and changes in nutritive value for large-round bales of alfalfa or alfalfa-grass hays made with or without a propionic-acid-based preservative. Materials and Methods: In Experiment 1, 18 large-round bales (83% alfalfa, 17% mixed grass) were produced (20.6% moisture) in a randomized complete block design with a 2 × 3 factorial arrangement of bale diameters (1.2 or 1.5 m) and preservative application strategies [fully automated, fully automated assuming a constant baling rate, or control]. For Experiment 2, 28 large-round bales of alfalfa hay were produced in an unbalanced, completely randomized design (20.2% moisture; 16 acid-treated, 12 controls). Results and Discussion: For Experiment 1, all measures of spontaneous heating differed (P = 0.037) between the 1.2- and 1.5-m bale diameters, with the larger diameter exhibiting greater maximum internal bale temperatures (46.1 vs. 41.6oC; P = 0.012), and greater total heating degree days > 30oC (HDD) during storage (334 vs. 106 HDD; P = 0.024). In Experiment 2, all 16 acid-treated bales initially exhibited heating suppression relative to control hays, but differed only numerically for total HDD (450 vs. 628 HDD; P = 0.223) after storage; within acid-treated hays, 9 of 16 bales incurred a secondary heating response, primarily after 25 d in storage. Implications and Applications: Bale size has a strong effect on preservative effectiveness, and the secondary and extended heating responses exhibited by some acid-treated hays partially explain the mixed overall responses to preservative application noted in some previous experiments.