Essential Oil Compounds as Additives for Rehydrated Corn Grain Silage

Essential Oil Compounds as Additives for Rehydrated Corn Grain Silage Álvaro Bernardo da Silva Neto, Greiciele Morais, Ariádna Patricia Ribeiro and Luiz Gustavo Nussio ESALQ Department of Animal Science, University of São Paulo, Piracicaba, SP, Brazil Keywords: aerobic stability, essential oils, fermentation, rehydrated corn grain silage. Introduction Essential oils have been experimented with as additives for forage silages with promising results such as enhanced aerobic stability and improvements in conservation quality. However, published trials are still limited to crude oils extracted from plants, and there is a lack of information regarding the use of essential oils as additives for grain silages. This study aimed to identify molecular compounds isolated from essential oils that could be promising as strategic additives for rehydrated corn grain silage (RCGS). Materials and methods Silages were made by rehydrating dry ground corn grains to 350 g/kg of moisture and packing (>1,000 kg/m3) in 5-L plastic buckets. Treatments were prepared as a factorial arrangement of 2 storage times (30 and 60 d) × fifteen strategies, being: control RCGS (CT); carvacrol at 200 (CAL), 600 (CAM) and 1,000 (CAH) mg/kg fresh matter (FM); cinnamaldehyde at 200 (CIL), 600 (CIM) and 1,000 (CIH) mg/kg FM; D-limonene at 200 (LIL), 600 (LIM) and 1,000 (LIH) mg/kg FM; citral at 200 (CRL), 600 (CRM) and 1,000 (CRH) mg/kg FM; commercial microbial inoculant (MI) containing Lentilactobacillus buchneri (1.12 × 105 cfu/g FM), Lactiplantibacillus plantarum (9.6 × 104 cfu/g FM) and Propionibacterium acidipropionici (1.12 × 105 cfu/g FM); and sodium benzoate at 2 g/kg FM (BZ). The MI and BZ strategies were considered positive controls. The RCGS were evaluated for dry matter (DM) losses, microbial and fermentative profile, and aerobic stability. Results The treatment of RCGS with sodium benzoate at 2 g/kg FM promoted higher quality of conservation, decreasing DM losses in the silo (Figure 1), and suppressing populations of yeasts and molds, which also markedly enhanced the aerobic stability (Figure 2). The treatment of RCGS with a microbial inoculant combining L. buchneri, L. plantarum and P. acidipropionici did not yield the expected results though, failing in achieve better outcomes for conservation and aerobic stability. Thus, we chose the BZ strategy as the positive control treatment to discuss the results for the strategies based on essential oil compounds in this study. Carvacrol decreased lactic acid production, especially at the higher doses (600 and 1,000 mg/kg FM), which compromised the acidification of RCGS, with CAM and CAH presenting the highest pH values in our study (4.1 and 4.2, respectively). The hampered acidification probably favored undesirable fermentations, as greater DM losses were observed (Figure 1) and even a favoring of Clostridium development occurred on the CAH silage, which presented an exceptionally high concentration of butyric acid (4,500 mg/kg DM). However, carvacrol showed promising results for aerobic stability, with CAH at 60 d of storage being able to emulate the effects of BZ (Figure 2). The CIH strategy was effective at inhibiting yeasts and was the only strategy besides BZ capable of suppressing fungi. Both CIM and CIH were able to decrease ethanol content. Curiously, the extended storage time from 30 to 60 d reduced the efficiency of CIH in suppressing yeasts, accompanied by a decrease in lactic acid content. It seems that storage time may be an important factor regulating the efficiency of cinnamaldehyde as an antimicrobial agent in grain silage. All strategies with cinnamaldehyde promoted lower pH values for RCGS at both storage times (ranging from 3.9 to 4.0), which probably enhanced the quality of conservation of the silages, as CIM and CIH were able to emulate the decreased DM losses observed for the BZ strategy (Figure 1). Only CIH managed to enhance aerobic stability of RCGS, although it was not able to emulate BZ (Figure 2). D-limonene did not prevent DM losses nor consistently improved aerobic stability with doses varying from 200 to 1,000 mg/kg FM. Citral also did not improve silage conservation quality nor its aerobic stability. Both compounds were deemed not promising as additive for RCGS. Conclusions Of the compounds tested in this study, only carvacrol and cinnamaldehyde proved promising as strategic additives for RCGS. Carvacrol enhanced aerobic stability with increasing doses, being able to emulate sodium benzoate when applied at 1,000 mg/kg FM in RCGS stored for 60 d, although this enhancement may be associated to the increased butyric acid production. Carvacrol, however, compromised the acidification and increased DM losses in the silo. Cinnamaldehyde decreased DM losses, being able to emulate sodium benzoate when applied at doses of 600 and 1,000 mg/kg FM. However, even the enhanced aerobic stability with the 1,000 mg/kg FM dose was not able to emulate sodium benzoate, and higher doses will be experimented in a future trial. D-limonene and citral did not promote consistent results desirable for RCGS within the doses and storage times evaluated in this study. References Foskolos, A.; Cavini, S.; Ferret, A.; Calsamiglia, S. 2016. Effects of essential oil compounds addition on ryegrass silage protein degradation. Can. J. Anim. Sci. 96:100-103. https://dx.doi.org/10.1139/cjas-2015-0025. Susanto, I.; Rahmadani, M.; Wiryawan, K.G.; Laconi, E.B.; Jayanegara, A. 2023. Evaluation of essential oils as additives during fermentation of feed products: a meta-analysis. Fermentation 9(7):583-596. https://doi.org/10.3390/fermentation9070583. Figure 1. DM loss of RCGS according to the treatments. Effect of strategy, P < 0.01; effect of storage time, P < 0.01; interaction strategy × storage time, P < 0.01. SEM = 0.15. Means with different letters differ by Tukey test (P < 0.05) within storage time (bars of same color). (*) Effect of storage time (P < 0.05) within the strategy. Figure 2. Aerobic stability of RCGS according to the treatments. Effect of strategy, P < 0.01; effect of storage time, P = 0.32; interaction strategy × storage time, P < 0.01. SEM = 6.5. Means with different letters differ by Tukey test (P < 0.05) within storage time (bars of same color). (*) Effect of storage time (P < 0.05) within the strategy. Contact Information: Luiz Gustavo Nussio, Email: [email protected]