Gas production from forages incubated in vitro with or without antibiotic and/or antifungal addition

LUCAS SANTOS; MARIANA P. MEZZOMO; CLAUDIO A. POZO; GILBERTO V. KOZLOSKI

Foz do Iguaçu

Congreso; 54 Annual Meeting of the Brazilian Society of Animal Science; 2017

Sociedade Brasileira de Zootecnia

The study was conducted to evaluate the interactive role of bacteria and fungi on forage degradation in vitro. In vitro assays were conducted with samples of Cynodon spp. and Lolium multiflorum as substrates. Dried and ground (1 mm screen) samples were weighed (1.5 g) in 160 mL flasks and incubated in vitro during 72 h in medium (80 mL buffer + 20 mL rumen inoculum) containing or not antimicrobial substances. A mixture of penicillin, chloramphenicol and streptomycin (500 mg L-1 of each) were used as antibiotic and cycloheximide (50 mg L-1) was used as antifungal. In vitro fermentations were conducted anaerobically in a water-bath slow-stir system at 39°C. Treatments were: antibiotic (Ab), antifungal (Af), negative control (i.e. without antimicrobials) or positive control (i.e. with both Ab and Af). Three assays were conducted, and three flasks were used for each forage type and treatment in each assay. Gas volume was measured at 3, 6, 9, 12, 24, 36, 48 and 72 hours of incubation. Data of the three flasks in each assay were averaged for analysis. The MIXED procedure of SAS was used for data analysis, using a variance-covariance model that included the fixed effects of forage type and treatments, and time of incubation as the covariate. Linear and quadratic interactions were tested and, by convenience, treatment means within specific times of incubation were also compared by contrast analysis. There was not significant interaction between forage type and treatments for any variable. There was a significant quadratic interaction (P < 0.05) between treatments and time of incubation. The gas production at 36 hours of incubation was, on average, 146, 130, 49 and 11 mL (s.e. = 13.8) and, at 72 hours of incubation, was 177, 164, 77 and 15 mL (s.e. = 15.9) for negative control, Af, Ab and positive control treatments, respectively. At either time of incubation 36 or 72 hours, gas volume in negative control was higher than in other treatments, and gas volume in positive control was lower than in other treatments (P < 0.05). Moreover, gas volume was always lower in Ab than in Af (P < 0.05). These results indicate that throughout 72 hours of in vitro fermentation bacteria had the most important role on forage degradation what, however, was increased by fungi activity. The mechanisms by which fungi interact with bacteria for degrading forage into the rumen needs to beelucidated.