Effects of extruded linseed on ruminal fermentation, rumen microbiota, and enteric methane emissions in lactating...

Extruded linseed (EL) supplementation is a recognized strategy to reduce enteric CH₄ emissions in dairy cows, although its mitigation potential may depend on diet composition. This study evaluated the impact of EL on production performance, CH₄ emissions, ruminal fermentation and microbiota in corn silage (CS)- and grass silage (GS)-based diets. Forty lactating Holstein Friesian cows (99 ± 41 DIM, 34.7 ± 5.2 kg milk, and mean parity of 3.2 ± 1.9) were used in an incomplete Latin square design with a 2 × 2 factorial arrangement: CS-based (CS:GS = 75:25) or GS-based (CS:GS = 25:75) diet, with or without EL supplementation (control; CTRL) providing 400 g crude fat/d. Each period lasted 35 d. Dry matter intake (Roughage Intake Control bins, Hokofarm Group), milk yield and composition, and CH₄ emissions (GreenFeed, C-Lock Inc.) were measured during the last 3 wk of each period. Rumen samples were collected for VFA analysis and metataxonomic profiling of bacteria, archaea, protozoa, and fungi. No interaction between EL supplementation and diet composition was observed. Compared with the CS-based diet, the GS-based diet increased CH₄ production, yield, and intensity by 5%, 6%, and 8%, respectively. On average, milk production and fat-and protein-corrected milk were2.1 kg/d and 1.8 kg/d lower, respectively, in cows fed the GS-based diet compared with the CS-based diet. The fermentation pattern shifted, with higher proportions of acetate (+1.4 µmol/mol) and butyrate (+1.1 mmol/mol) and a lower propionate proportion (-0.06 mmol/mol) in cows fed the GS-based diets compared with the CS-based diet. The α-diversity of bacteria, fungi, and protozoa was higher in GS-based diet compared with the CS-based diet. Across diets, supplementation of EL reduced CH₄ production and intensity by 5% and 8%, respectively. Although β-diversity of bacterial and archaeal communities was affected, only minor compositional changes were detected. The EL supplementation numerically increased net energy intake, resulting in a higher milk yield (+1.1 kg/d) compared with CTRL. At the applied inclusion level, CH₄ mitigation by EL was mainly the result of a reduced fermentable OM intake, rather than a shift in fermentation pattern or rumen microbiota.