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

Abstract

<p><i>Asparagopsis taxiformis</i> (<b><i>Asparagopsis</i></b>) has been shown to be highly efficacious at inhibiting the production of methane (<b>CH₄</b>) in ruminants. To date, <i>Asparagopsis</i> has been primarily produced as a dietary supplement by freeze-drying to retain the volatile bioactive compound bromoform (<b>CHBr₃</b>) in the product. Steeping of <i>Asparagopsis</i> bioactive compounds into a vegetable oil carrier (<b>Asp-Oil</b>) is an alternative method of stabilizing <i>Asparagopsis</i> as 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 <i>Asparagopsis</i> derived CHBr₃/kg dry matter intake (DMI), respectively (in addition to a zero CHBr₃ canola 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 CH₄ emissions 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 CH₄ yield (g CH₄/kg DMI, <i>P</i> = 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 (<i>P</i> = 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 (<i>P</i> > 0.10). There were no differences in animal production and carcass parameters (<i>P</i> > 0.10). There was no detectable CHBr₃ in feces or any carcass samples (<i>P</i> > 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 CH₄ emissions and yield by up to 99% within the range of inclusion levels tested.</p>