doi:10.5424/sjar/2021192-17728engAmanzougarene, ZYuste, SFondevila, MEffect of pre-activated Saccharomyces cerevisiae or malate salts on fermentation of ground barley grain under in vitro conditions simulating intensive ruminant feedingART-2021-126442Aim of study: To determine the dose response of Saccharomyces cerevisiae on rumen fermentation of concentrates, and to compare it with the effect of malate salts. Material and methods: S. cerevisiae (0.7, 1.4 and 2.1 mg/g) and malic acid salts (4, 8 or 12 mg/g) were added to barley and compared with barley alone (CTL), in three 24 h in vitro incubation series, using rumen inocula from beef cattle receiving a high concentrate diet. Yeasts were pre-activated by aerobic incubation for 24 h at 30 degrees C. Incubation pH was recorded at 8 and 24 h and volatile fatty acids (VFA) and lactate at 8 h were analysed. Main results: Gas produced with S. cerevisiae was higher than malate (p<0.001). Yeast addition linearly (p<0.01) and quadratically (p<0.05 at 4 h and from 10 to 18 h) increased gas production, but no dose response to malate levels was observed. Dry matter disappearance at 24 h was not affected by S. cerevisiae but increased linearly with malate. Microbial mass linearly increased with the level of yeast (p<0.01) and malate (p=0.09). Adding yeasts did not affect 8 h total VFA concentration compared with CTL, but linear valerate (p<0.01) and butyrate (p=0.092) increases, and a decrease of acetate (p=0.064) were detected. Malate salts linearly increased (p<0.05) total VFA concentration but did not affect VFA proportions. Research highlights: Addition of active yeasts linearly increased barley fermentation and microbial synthesis, whereas the effect of malate salts was of minor magnitude.2021http://zaguan.unizar.es/record/11888210.5424/sjar/2021192-17728http://zaguan.unizar.es/record/118882oai:zaguan.unizar.es:118882info:eu-repo/grantAgreement/ES/FEDER/UIDB/04011/2020info:eu-repo/grantAgreement/ES/MECD/FPU-Formación de profesorado universitarioinfo:eu-repo/grantAgreement/ES/MINECO-DGA-FSE/AGL2013-46820Spanish Journal of Agricultural Research 19, 2 (2021), e06SCO2 [7 pp]byhttp://creativecommons.org/licenses/by/3.0/es/info:eu-repo/semantics/openAccess