Bioactive metabolites of Asparagopsisstabilized in canola oil completely suppress methane emissions in beef cattle fed a feedlot diet

Asparagopsis taxiformis(Asparagopsis) has been shown to be highly efficacious at inhibiting the production of methane (CH4) in ruminants. To date, Asparagopsishas been primarily produced as a dietary supplement by freeze-drying to retain the volatile bioactive compound bromoform (CHBr3) in the product. Steeping of Asparagopsisbioactive compounds into a vegetable oil carrier (Asp-Oil) is an alternative method of stabilizing Asparagopsisas a ruminant feed additive. A dose–response experimental design used 3 Asp-Oil-canola oil blends, low, medium, and high Asp-Oil which provided 17, 34, and 51 mg Asparagopsisderived CHBr3/kg dry matter intake (DMI), respectively (in addition to a zero CHBr3canola oil control), in a tempered-barley based feedlot finisher diet, fed for 59 d to 20 Angus heifers (five replicates per treatment). On four occasions, live weight was measured and CH4emissions were quantified in respiration chambers, and blood, rumen fluid, and fecal samples were collected. At the end of the experiment, all animals were slaughtered, with carcasses graded, and samples of meat and edible offal collected for testing of consumer sensory qualities and residues of CHBr3, bromide, and iodide. All Asp-Oil treatments reduced CH4yield (g CH4/kg DMI, P= 0.008) from control levels, with the low, medium, and high Asp-Oil achieving 64%, 98%, and 99% reduction, respectively. Dissolved hydrogen increased linearly with increasing Asp-Oil inclusion, by more than 17-fold in the high Asp-Oil group (P= 0.017). There was no effect of Asp-Oil treatment on rumen temperature, pH, reduction potential, volatile fatty acid and ammonia production, rumen pathology, and histopathology (P> 0.10). There were no differences in animal production and carcass parameters (P> 0.10). There was no detectable CHBr3in feces or any carcass samples (P> 0.10), and iodide and bromide residues in kidneys were at levels unlikely to lead to consumers exceeding recommended maximum intakes. Overall, Asp-Oil was found to be safe for animals and consumers of meat, and effective at reducing CH4emissions and yield by up to 99% within the range of inclusion levels tested.A feed ingredient containing bioactive metabolites of Asparagopsisstabilized in canola oil was able to virtually eliminate methane emissions from grain-fed cattle, without impacting animal health or production, or consumer safety.Red seaweed, Asparagopsis taxiformis(Asparagopsis), has been shown to be highly effective at inhibiting the production of methane (CH4) in ruminants. An alternative to feeding whole, freeze-dried Asparagopsisis steeping the biomass in vegetable oil to stabilize the bioactive compounds (Asp-Oil) and feeding Asp-Oil to ruminants as a component of their dietary intake. This experiment measured the CH4reduction potential and safety of Asp-Oil in a trial with 20 Angus heifers, fed iso-fat feedlot diets containing one of the three levels of Asp-Oil, or a control oil. Compared to the control, bromoform inclusion levels of 17, 34, and 51 mg/kg of dry matter (DM; low, medium, high) reduced CH4yield (g CH4/kg DM intake) by 64%, 98%, and 99%, respectively. There were no effects on animal production or carcass characteristics. There were no impacts on animal health, welfare, or rumen function. Carcasses were safe for human consumption, and there was no bromoform detected in any carcass samples. Overall, Asp-Oil was found to effectively reduce CH4emissions and is safe for animals and consumers of meat and edible offal.