Nutritive value and storage characteristics of large-round bales of alfalfa-grass or perennial-grass hays treated with a propionic acid-based preservative at elevated application presets

Authors: Coblentz, Wayne; AKINS, MATTHEW - University Of Wisconsin

Submitted to: Applied Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/20/2021
Publication Date: 3/22/2022
Citation: Coblentz, W.K., Akins, M. 2022. Nutritive value and storage characteristics of large-round bales of alfalfa-grass or perennial-grass hays treated with a propionic acid-based preservative at elevated application presets. Applied Animal Science. 38(2):84-97. https://doi.org/10.15232/aas.2021-02243.
DOI: https://doi.org/10.15232/aas.2021-02243

Interpretive Summary: Unpredictable weather patterns and/or humid weather frequently force hay producers to make difficult management choices related to the harvest and storage of their forage crops. Our objectives were to evaluate large-round bales treated with a propionic-acid-based preservative applied with a state-of-the-art applicator system programed to apply 50% greater rates than normal manufacturer presets; furthermore, these evaluations included two studies conducted at the upper (30.5%) and lower limits (18.4%) of moisture recommended for effective preservative use. Application of a propionic-acid-based preservative using a 50% increase in standard factory preset rates for the 3 application pumps embedded in the applicator system was effective at reducing the intensity of spontaneous heating during the first month of storage for round-baled alfalfa-grass hays baled at approximately 30% moisture. While spontaneous heating was reduced sharply during the first month of storage, total heating units incurred within treated hays did not differ from controls when considered over the entire 131-day storage period. Modest benefits were observed in treated hays with respect to final concentrations of acid-detergent lignin, heat-damaged protein, energy density, and in-vitro dry matter disappearance, but the cost of applying high rates of preservative renders this approach to nutrient preservation questionable. For perennial cool-season grass hays baled at 18% moisture in September, there was little evidence of nutrient loss in untreated hays, and application of the propionic-acid-based preservative provided no additional benefit with respect to nutrient retention. This suggests that a common 18% moisture target for safe storage of round bales is appropriate for baling late-summer hays in the north-central USA.

Technical Abstract: Objectives: Our objectives were to evaluate the storage characteristics and changes in nutritive value for large-round bales of alfalfa-grass or perennial-grass hays treated with a propionic-acid-based preservative applied at greater-than-recommended rates when compared against untreated control hays. Materials and Methods: In Experiment 1, 21 large-round bales (1.2 × 1.5 m; 30.5 ± 1.40% moisture; 88% alfalfa, 12% grass) were produced in a completely randomized design with 2 treatments. Bales either received a propionic-acid-based preservative at 1.0 ± 0.41% of wet bale weight (N = 11), or no preservative (N = 10), and were stored outdoors on wooden pallets for 131 d. Experiment 2 was conducted similarly; 26 bales of mixed, perennial-grass hay (1.2 × 1.5 m; 18.4 ± 1.40% moisture) were either treated with a preservative at 0.25 ± 0.104% of wet bale weight (N = 15) or were untreated (N = 11) and stored in an identical manner for 40 d. Results and Discussion: In Experiment 1, application of the preservative reduced maximum internal bale temperatures during the first 30 d of storage compared to untreated control hays (51.8 vs. 60.6oC; P < 0.001); similarly, heating degree days > 30oC (HDD) were less for treated hays during the same initial (30-d) time interval (441 vs. 716 HDD; P = 0.001). However, total HDD after 131 d of storage did not differ across treatments (P = 0.426), largely because of the tendency for greater accumulated HDD in treated bales from 31 to 131 d in storage (1105 vs. 761 HDD; P = 0.085). Final energy density (NEl) was greater (P = 0.030) for treated hays compared to untreated control hays (1.26 vs. 1.21 Mcal/kg DM), but both treatments were depressed from initial pre-storage estimates (overall mean = 1.37 Mcal/kg DM). For Experiment 2, there were no differences (P = 0.185) between treatments for any post-storage measure of nutritive value. Implications and Applications: For bales made at 30.5% moisture, application of a propionic-acid-based preservative at greater than recommended rates effectively reduced spontaneous heating during the first month of bale storage, and modestly improved post-storage energy density; however, any nutritional benefit from treatment was modest, and energy density was still subject to measurable reductions relative to pre-storage estimates.