The macroalga Asparagopsis taxiformis decreases dry matter intake and milk production in dairy cows

ABSTRACT: Studies with sheep and cattle have identified the macroalga Asparagopsis taxiformis (AT) as a potent methane-mitigating feed additive but have also raised concerns related to bromoform's (a halogenated compound responsible for the antimethanogenic effect of AT) stability over prolonged storage. Previously, our laboratory conducted a study in which the effect of AT on enteric CH4 diminished over time. This effect had not been previously reported and warranted further investigation. The study was conducted with 18 Holstein cows in a replicated 3 × 3 Latin square design with 28-d periods. Treatments were control (basal diet), basal diet + 0.50% AT, and basal diet + 0.75% AT (feed DM basis). Methane emission was measured using the GreenFeed system. At the beginning of the experiment, bromoform concentration in AT was 4.41 mg/g DM. Daily CH4 emission decreased up to 30% with increasing AT dose. Inclusion of AT also decreased DMI by up to 22%, resulting in no effect on CH4 yield (g CH4/kg DMI). Milk true protein and lactose concentrations decreased up to 4% and 2% by AT, respectively. Asparagopsis taxiformis decreased milk fat yield up to 13%. Milk true protein and lactose yields were decreased up to 15% and 14% by AT, respectively, resulting in a decrease in ECM of up to 14%. Methane intensity (g CH4/kg of ECM) decreased by AT up to 18%. Additionally, there was a decrease in BW in cows fed AT, compared with the control. In conclusion, AT stored over 20 mo and included at up to 0.75% (feed DM basis) in the diet of dairy cows decreased daily CH4 emission but did not affect CH4 yield and decreased DMI and milk yield in mid-lactation dairy cows. These data confirm previous observations of inconsistent effects of AT on CH4 emission metrics and negative effects of AT on feed intake and productivity.