Inclusion of rapeseed cake or oil in the diet of beef cattle reduces enteric methane emissions without affecting animal performance.

The global methane (CH4) pledge aims to reduce anthropogenic CH4 emissions by 30% by 2030. Oilseed rape (Brassica napus L), a break crop with 40 million ha cultivated globally in 2022, produces fatty acid-rich by-products that could potentially reduce rumen methanogenesis while enhancing meat fat composition. The study objective was to examine the effects of fatty acid supplementation from rapeseed ingredients on DM intake (DMI), average daily gain, gaseous emissions, haematology, rumen fermentation pattern, and fatty acid content of the longissimus dorsi muscle of beef cattle fed a mixed forage and concentrate diet. Fifty-four crossbred Charolais steers and heifers with a mean BW of 384 kg (SD 39.5) were offered concentrates at 60% of total DMI containing either an unsupplemented control (CON), rapeseed cake (RSC), or rapeseed oil (RSO). Rapeseed cake and oil dietary inclusion (35.0 and 6.1%, respectively, in concentrates) were balanced on oil, total fatty acid, polyunsaturated fatty acid, and monounsaturated fatty acid content. Cattle were offered ad libitum grass silage. Feed intake and gaseous emissions were recorded over 71 days after a 17-day baseline period. Animals were weighed weekly. Ultrasonic muscle and fat deposition were recorded during the baseline and on day 70. Blood and rumen digesta samples were collected during the baseline and on days 36 and 71. Biopsies of the longissimus dorsi muscle were collected on day 72. Dietary treatment did not affect DMI (P = 0.38). The RSO group had a higher average daily gain than RSC; however, there was no difference compared to CON (1.22, 1.05, and 1.18 kg/day, respectively) (P = 0.02). The RSC and RSO treatments decreased enteric CH4 by 17.7 and 16.0 g/day, respectively, compared to CON (P < 0.001). Hydrogen and carbon dioxide production between groups was similar (P = 0.18 and P = 0.06, respectively). Serum high- and low-density lipoprotein cholesterol concentrations increased for RSC and RSO (P < 0.05). Although supplementing cattle with RSO lowered rumen pH compared to RSC (P = 0.003), there were no observed dietary effects on ammonia-nitrogen or volatile fatty acid concentrations in the rumen (P > 0.05). Treatment did not affect muscle and fat accretion or muscle fatty acid composition (P > 0.05). Findings suggest that dietary supplementation with RSO or RSC has anti-methanogenic potential with similar animal performance compared to an unsupplemented control. Dietary supplementation with rapeseed by-products could be readily implemented as a management strategy to enhance beef system sustainability.