PSXIII-3 Regrowth interval and propionic acid effects on warm-season grass silage nutritive value and fermentation characteristics

Abstract Warm-season perennial grass species are the main forages preserved as silage or haylage by livestock producers in Florida; however, the nutritive value and silage fermentation parameters are often less than desirable. The objective of this study was to investigate the effects of regrowth interval, propionic acid, and forage species on silage nutritive value and fermentation parameters. The study was conducted in Ona, FL in July and August 2021 and 2022. Treatments were the factorial combination of three forage species [Jiggs bermudagrass (Cynodon dactylon L.), ‘Camello’ brachiariagrass (Urochloa spp.), or Spain guineagrass (Megathyrsus maximus (Jacq.) B.K. Simon & S.W.L. Jacobs)], two regrowth intervals (3 or 6 wk), and propionic acid [0.5% or 0 (control)], distributed in a randomized complete block design with 4 replicates. Forage was harvested and immediately packed into a mini-silo at a density of approximately 190 kg DM/m3. Camello and Spain had less DM (24 vs. 30%; P < 0.01), CP (8.0 vs. 10.7%; P < 0.01), but greater NDF (70 vs. 68%; P < 0.01), ADF (41 vs. 38%; P < 0.01), and in vitro digestible OM concentration (57 vs. 52%; P = 0.04) than Jiggs. There were no differences in fermentation characteristics among species. Forage harvested at 3-wk regrowth interval had less DM (24 vs. 29%; P < 0.01), NDF (68 vs. 71%; P < 0.01), ADF (38 vs. 40%; P < 0.01) but greater CP (10.8 vs. 8.3%; P < 0.01) and in vitro digestible OM (56 vs. 52%; P = 0.03) than 6 wk. There was no effect (P > 0.05) of regrowth interval on fermentation characteristics. Forage treated with propionic acid had greater DM (27 vs. 25%; P < 0.01), CP (9.6 vs. 9.0%; P < 0.01), lactic acid (4.3 vs. 3.1%; P < 0.01), and propionic acid concentrations (1.8 vs 0.1%; P < 0.01) but decreased pH (4.2 vs. 4.6; P < 0.01), ammonia (12 vs. 18% CP; P < 0.01), acetic acid (1.5 vs. 2.0%; P < 0.01), and butyric acid concentrations (0.2 vs. 1.5%; P < 0.01). Propionic acid affected bacterial population abundance by decreasing Clostridium (0.6 vs. 5.3%; P < 0.01) and Enterobacteria (3.0 vs. 11.1%; P < 0.01) and increasing Lactobacillus (45.0 vs. 32.7%; P = 0.04) and Bacillus (0.35 vs. 0.15%; P < 0.01). Forage species and regrowth interval were influential on silage nutritive value while propionic acid improved fermentation characteristics.