The effect of a water-based delivery of an Ascophyllum nodosum extract on animal performance, rumen microbiota, fermentation, and methane emissions of zero-grazed beef steers

This study evaluated the effects of an Ascophyllum nodosum (ASC) extract delivered via a water-based system on animal performance, rumen microbiota, fermentation, and methane (CH 4 ) emissions in beef steers. Thirty dairy-beef steers were randomly allocated to one of two dietary treatments ( n = 15) for a 70-d period. Treatments consisted of either ad libitum zero-grazed grass ( CTR ; no extract) or ad libitum zero-grazed grass plus an ASC extract ( ASCE ) supplemented at 1.5% of dry matter intake (DMI), administered via a water-based system. Additionally, all steers were offered a maximum of 1.4 kg/d of concentrate. Methane was measured throughout the study using the GreenFeed emissions monitoring system (GEM). A feed intake estimation period was conducted during week 5 and 10, while rumen fluid samples were collected on d-33 and d-68 for rumen microbiota and fermentation analysis. There was no difference between treatments for total DMI, average daily gain (ADG), or diet digestibility. Methane production was similar between treatments, averaging 206.6 g/d for CTR and 204.6 g/d for ASCE. Methane yield (g/kg DMI) and intensity (g/kg ADG) were also unaffected, averaging 24.8 g/kg DMI and 130.8 g/kg ADG, respectively. The proportion of butyrate was lower, and ammonia-nitrogen (NH 3 -N) concentration was higher in ASCE-treated steers. Microbial abundances were unaffected, with Bacteroidota (51%) and Firmicutes (38.3%) being the most abundant phyla across both treatments. In conclusion, ASCE supplementation did not impact animal performance, CH 4 emissions or rumen microbiota.