The effects of feeding liquid or pelleted formulations of Asparagopsis armata to lactating dairy cows on methane production, dry matter intake, milk production and milk composition

Asparagopsis armata has been reported to have strong antimethanogenic effects when fed to dairy cows. The aim of this study was to evaluate the effect of a liquid and a pelleted formulation of A. armata when fed to lactating dairy cows as a supplemental feed twice daily at milking on i) enteric methane emissions, milk yield and dry matter intake (DMI), and ii) presence of halogenated compounds in milk, urine, faeces, and blood. Forty lactating, multiparous, Holstein-Friesian cows (117 +/- 20.2 days in milk) were randomly allocated one of four treatments; 1) CON1: basal diet plus liquid supplement without A. armata, 2) AA1: basal diet plus liquid supplement with A. armata, 3) CON2: basal diet plus pellet supplement without A. armata, and 4) AA2: basal diet plus pellet supplement with A. armata. The liquid and pelleted supplements were offered twice daily for 34 days. Supplements were offered with a grain mix during each milking. The basal diet consisted of vetch hay ad libitum and 6.15 kg dry matter (DM)/d of a grain mix fed as 3.07 kg DM in the dairy per milking. Cows given the AA1 treatment received 298 mg bromoform per day while cows on the AA2 treatment received 293 mg bromoform per day. Individual forage DMI were measured daily via electronic monitoring of individual cows at the feed bins. Methane emissions were measured using the modified sulphur hexafluoride tracer technique on the last 5 days of the experiment. Feeding the A. armata formulations showed no effect on total DMI, forage DMI, concentrate DMI or milk yield. Methane production (g CH4/d), methane yield (g CH4/kg DMI) and methane intensity (g CH4/kg energy corrected milk) were reduced by about 20 % for both the liquid and the pelleted A. armata formulations. Feeding the A. armata formulations led to increased bromoform concentrations in milk (-2.0 mu g/L) but were well below the limit for safe consumption (100 mu g/L). It is concluded that both formulations were effective in reducing enteric methane emissions and that milk from cows fed these A. armata formulations is safe for human consumption.