Asparagopsis meal reduces enteric methane emissions of feedlot beef cattle without impact on productivity or meat and carcass quality

Asparagopsis supplementation induces strong antimethanogenic effects in ruminant animals by consistently reducing enteric methane (CH 4 ) emissions in controlled feeding environments. This study has advanced the utility of feeding dried Asparagopsis products (Asp-Meal) in beef feedlots. The experiment was conducted at an Australian-certified feedlot, using Greenfeed emissions monitoring, and 64 heifers of mixed breeds (aged 12 – 18 months, initial BW 384 ± 27.8 kg) were offered diets of Control (no Asp-Meal) or Asp-Meal [30 mg bromoform/kg DMI] for 74-days. A pilot study was used to determine the inclusion rate of 30 mg bromoform/kg dry matter intake (DMI). Asp-Meal inclusion induced CH 4 mitigation of 67.9 % for production (g/day), 67.0 % for yield (g/kg DMI), and 61.7 % for intensity (g/kg average daily weight gain), however, it should be noted that Asp-Meal CH 4 measurements were consistently lower than the limit of detection (40 g/d) of the Greenfeed sensors which could have confounded antimethanogenic accounting. Additionally, no negative impacts were induced on animal growth performance, carcass quality, or rumen epithelium confirmed with macroscopic gross and histological examinations. No bromoform was found in meat, kidney, or liver of either Control or Asp-Meal cattle. Iodide and bromide levels for Control and Asp-Meal groups were within acceptable daily intake ranges for human consumption, however, were elevated by Asp-Meal in meat, kidney, and liver. Commercial application of Asparagopsis products for feedlots would benefit from elucidation of breed effect on enteric CH 4 reduction and productivity therefore variable breed studies are warranted. This study demonstrates that Asp-Meal is an efficient antimethanogenic feed additive for methane emissions management from feedlot beef production without negative impact on production or food quality.