Resumen: Aim of study: To isolate fibre effect from other factors when comparing fibrous sources, the rumen fermentation pattern of extracted cell walls was studied. Material and methods: Cell wall fractions from soybean hulls (SH), sugarbeet pulp (BP), palm kernel cake (PK), oat hulls (OH), dehydrated alfalfa meal (DA) and barley straw (BS) were incubated in four 48 h series. Main results: Cell wall extraction efficiency was +/- 0.07 units over the neutral detergent fibre content, except for PK, which recovery was 0.20. Gas produced from BP and SH was higher (p<0.05) from 6 h. PK behaved similarly to SH from 6 to 24 h but maintained constant thereafter, whereas gas volume from OH was the lowest from 24 to 48 h (p<0.05). All substrates recorded a maximum rate of gas production at 12 h, except OH, for which fermentation was constant on time. The organic matter disappearance after 48 h incubation agreed with these results, being higher with BP and SH, whereas OH was the lowest (p<0.05). The proportion of methane in total gas produced was higher in OH than BP at 36 and 48 h (p<0.05). The highest total VFA concentration was recorded with BP (p<0.05). Propionate proportion was enhanced from BP, BS and SH, and that of butyrate was higher with PK and OH, whereas no differences among substrates were recorded in acetate proportion. Research highlights: Fermentation of the cell wall fraction of fibrous feeds is not directly linked to its chemical composition, not even to its lignin proportion. Idioma: Inglés DOI: 10.5424/sjar/2021192-17653 Año: 2021 Publicado en: Spanish Journal of Agricultural Research 19, 2 (2021), e0605 [9 pp] ISSN: 1695-971X Factor impacto JCR: 1.233 (2021) Categ. JCR: AGRICULTURE, MULTIDISCIPLINARY rank: 37 / 60 = 0.617 (2021) - Q3 - T2 Factor impacto CITESCORE: 1.9 - Agricultural and Biological Sciences (Q3)