PSVIII-20 Regrowth interval, forage species, and propionic acid effects on DM and NDF digestibility of warm-season perennial grass silage.

Abstract The objective of this study was to evaluate the effects of regrowth interval, forage species, and propionic acid treatment on warm-season perennial grass silage. The study was conducted in Ona, FL From July to September 2023. Treatments were the split-split-plot arrangement of three forage species [‘Camello’ brachiarigrass (Urochloa spp.), Spain guineagrass (Megathyrsus maximum), and Jiggs bermudagrass (Cynodon dactlyon)], two regrowth intervals (3 or 6 weeks), and propionic acid [0.5 % green weight or 0 (control)] distributed in a randomized complete block design with 4 replicates. Plots (5 x 5 m) were the experimental units. Samples of each treatment were incubated in two steers (Bos sp.) for 0, 3, 6, 9, 12, 24, 48, and 72 h and the DM and NDF disappearance was fitted in the non-linear model proposed by Ørskov and McDonald (1979). The DM and NDF fractions were described as A, rapidly degradable; B, potentially degradable; and C, undegradable. Potential DM and NDF degradability were calculated by fixing the particle turnover at 0.02 h-1. There was a forage species × regrowth interval interaction (P < 0.05) on DM potential degradability (PD), fractions A, B, and C. The interaction occurred because there was no difference in DM PD (54 vs. 52%), fraction A (22 vs. 23%), fraction B (49 vs. 48%), and fraction C (29 vs. 29%) in brachiarigrass from 3 to 6 weeks regrowth interval; however, DM PD, fractions A and B decreased, and fraction C increased from 3 to 6 weeks in bermudagrass (51 vs. 40%; 23 vs. 21%, 37 vs. 31; and 40 vs. 48%) and guineagrass (52 vs. 46%; 22 vs. 18%, 51 vs. 46%; and 27 vs. 36%). Similarly, there was a forage species × regrowth interval interaction (P < 0.05) on NDF PD, fractions B and C, but there was no effect on fraction A (P = 0.36). The NDF PD and fractions B and C did not differ between 3 and 6 weeks in brachiarigrass (43 vs. 40%; 56 vs. 53%, and 36 vs. 39%) and guineagrass (41 vs 39%, 52 vs. 50%, 37 vs. 41%); however, NDF PD and fraction B decreased, and fraction C increased in bermudagrass (43 vs. 34%, 56 vs. 44%, and 34 vs. 47%). There was no effect (P > 0.26) of propionic acid treatment on DM PD, NDF PD, and DM or NDF fractions. Brachiariagrass is a desirable warm-season perennial grass to be ensiled due to the flexibility of harvesting in advance maturity with no negative effects on digestibility. Propionic acid is a common additive to enhance fermentation characteristics of warm-season perennial grasses and has no detrimental effect on silage digestibility.