Effects of Lignocellulolytic enzymes produced by Pleurotus ostreatus on the nutritive value of whole-plant corn silage

RESUMO

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ABSTRACT

Three experiments were carried out to examine the effect of lignocellulolytic enzymes on the nutritive value of whole-plant corn silage (WPCS). In experiment 1, we examined the effect of spent substrate from Pleurotus ostreatus cultivation (SSPO) on the chemical composition, antioxidant capacity, lignin monomers, and in vitro 5 digestibility of WPCS. In experiment 2, we evaluated the performance of lactating goats fed WPCS treated with different levels of SSPO. In experiment 3, we verified the activity of an enzymatic complex at different pH and the effects of adding increasing levels of that enzymatic complex produced by Pleurotus ostreatus on the fermentative profile, chemical composition, and ruminal digestibility along of the days on the onset of fermentation of WPCS. In experiment 1, four levels of lignocellulolytic enzymes from spent substrate of Pleurotus ostreatus were tested in a completely randomized design: 0, 10, 20, and 30 mg of lignocellulosic enzymes/kg of fresh matter, and four replicates per treatment (vacuum-sealed bags). The bags were opened 60 d after ensiling. The NDF, ADF, lignin, and cellulose concentration decreased quadratically. At the nadir point, SSPO decreased NDF by 14.1%, ADF by 19.5%, lignin by 9.07%, and cellulose by 22.1% compared to the untreated silage. Therefore, SSPO led to a quadratic increase in IVDMD of WPCS (+10.3 % at vertex). In experiment 2, WPCS treated with three enzyme levels (0, 10, or 30 mg/kg fresh matter, chosen based on experiment 1) were fed to lactating goats as part of TMR. Nine lactating Saanen goats (62.68±7.62 kg BW; 44±8 days in milk; 2.91±0.81 kg of milk/day, mean±SD) were assigned to three 3 × 3 Latin squares. Intake and digestibility of dry matter and nutrients, microbial protein syntheses, and milk production and composition were examined. The SSPO increase the in vivo total-tract ADF digestibility quadratically. Additionally, the concentration of polyphenols in milk increased linearly with the addition of SSPO in WPCS; however, no other differences were detected among treatments. In experiment 3, the lignocellulolytic enzymatic complex was obtained through in vitro cultivation of Pleurotus ostreatus, and the activities of laccase, lignin peroxidase, manganese peroxidase, endo and exoglucanase, xylanase, and mannanase were determined at pH 3, 29 4, 5, and 6. Following, five different enzymatic complex levels were tested in a completely randomized block design: 0; 9; 18; 27, and 36 mg of lignocellulosic enzymes/kg of fresh matter (FM) of whole-plant corn, with four replicates per treatment (vacuum-sealed bags). The bags were opened after 1, 2, 3, and 7 d of ensiling to evaluate the onset of fermentation and after 30 d of storage to evaluate the fermentation, chemical composition, and in situ digestibility of WPCS. Laccase showed highest activity at pH 5 (P < 0.01), whereas manganese peroxidase and lignin peroxidase had a higher activity at pH 4 (P < 0.01;< 0.01, respectively). There was no interaction between the enzymatic complex and days of fermentation (P > 0.11). The concentration of WSC decreased quadratically at the onset of fermentation (P = 0.02) due to its consumption that led to a quadratic increase of lactic acid (P = 0.01) and a linear increase of acetic acid (P = 0.02). As a result of increasing those organic acid concentrations, pH decreased quadratically (P = 0.01). Lignin concentration decreased linearly (P = 0.04) with the enzymatic complex at 30 d of storage. The collective interpretation of these results leads to the conclusion that 10 mg of lignocellulolytic enzymes from SSPO per kg of FM of WPC presented the best effect in silage production due to more evident reduction in NDF, ADF, and lignin concentration and increased ADF digestibility of lactation goats