Some species of red seaweed have been shown to reduce methane emissions by more than 80% in vitro and in sheep.

Now, researchers with the University of California-Davis, Stanford University and CSIRO Agriculture & Food in Queensland, Australia, have conducted a study with the objective of determining the effective dose of the seaweed Asparagopsis armata and quantifying its effect on enteric methane yield in regard to methane per unit of dry matter intake (DMI), milk production and feed conversion efficiency (FCE) in lactating dairy cattle in vivo

E. Kebreab of the University of California presented the findings during the American Dairy Science Assn. annual meeting in Knoxville, Tenn.

For the study, 12 post-peak-lactation multiparous Holstein cows producing 34.7 ± 5.9 kg/day milk were randomly allocated to one of three treatments in a 3 × 3 Latin square design. The experiment contained three periods: 14 days of measurement, with seven days of washout in between. Cows were fed the same basal diet, with treatment 1 used as the control and treatments 2 and 3 supplemented with the tetrasporophyte phase of A. armata at 0.5% (low supplement [LS]) or 1% (high supplement [HS]) on a grams of organic matter (OM) of seaweed per grams OM basis. The doses were determined through a pretrial in which the cows were fed 0.0%, 0.25%, 0.5%, 1.0% or 1.5% of A. armata.

The research found that there was a significant (P < 0.001) reduction of enteric methane above 0.5%; however, above 1.0%, DMI was reduced. Effects of A. armata on enteric methane yield, DMI and milk production were determined using the lmer function for linear mixed model analysis in R statistical software (version 3.4.4). Supplementation of A. armata resulted in a significant linear reduction in enteric methane yield (P < 0.001).

The LS and HS treatments reduced enteric methane yield by 16% and 48%, respectively. Hydrogen emissions (per unit of DMI) significantly (P < 0.001) increased by 57% and 306% for the LS and HS treatments, respectively, compared with the control, the researchers said.

Carbon dioxide production as a proportion of DMI also increased 5.7% and 31.5% (P < 0.01) in the LS and HS treatments, respectively. There was a linear decrease of 7.4% and 31.3% (P < 0.001) in DMI for the LS and HS treatments, respectively. However, there was no reduction in milk production (P = 0.56). Consequently, FCE increased linearly (P < 0.001), with the HS diet increasing FCE 49.5%, the researchers said.

According to the researchers, this is the first study in dairy cattle supplementing the seaweed A. armata that has shown a reduction in enteric methane yield by more than 40% at a 1.0% inclusion rate and significantly increased the FCE.