EFFECTS OF THE MACROALGA Asparagopsis taxiformis ON ENTERIC METHANE EMISSION AND LACTATIONAL PERFORMANCE OF DAIRY COWS

The macroalga, Aparagopsis taxiformis  (AT)  is a  source of multiple  halogenated compounds and  has been shown to decrease  enteric methane (CH₄) production in vitro and in sheep.  One in vitro and two in vivo studies were conducted to determine the antimethanogenic  effect  of AT in lactating dairy cows. In vitro , 10 treatments were tested in  repeated  24-h incubations with ruminal inoculum collected from two lactating Holstein cows. Treatments were: control (no additives), AT  included at 0.25, 0.5, 0.75, 1.0 and 1.5% of feed dry matter (DM) and bromoform (CHBr₃), the active compound in AT, equivalent to CHBr₃  found in AT dosed at 0.25, 0.5, and 1.5% (DM basis) .  A  short-term in vivo study (Exp. 1) was conducted with six lactating Holstein cows .  AT inclusion rates  were 0, 0.25, 0.50 , and 0.75% of feed DM intake (DMI) . Each experimental period consisted of 7-d diet adaptation and 3-d sampling, followed by a 7-d washout period. Experiment 2 (Exp. 2) was conducted with 20 lactating  Holstein cows in a  replicated  4 × 4 Latin s quare design with four 28-d periods. Treatments were control (basal diet), 0.25% AT, 0.50% AT, and 2.0% oregano  leaves of feed DMI .  The first 21 d  of each period were for diet adaptation and the last 7-d for sample collection. Enteric CH₄ emission was measured 8 times over 3- d using the GreenFeed system. Data were analyzed using the REG (in vitro) and MIXED (in vivo ) procedures of SAS. In the in vitro experiment, AT decreased CH₄ yield  quadratically [ P  = 0.02 ; 13.3 , 13.0 , 13.5 , 10.8 , 7.3 , and 1.2 mL CH₄ /g feed DM (SEM = 1.56) for control, 0.25, 0.5, 0.75, 1.0, and 1.5% AT, respectively]. CHBr₃ decreased CH₄ yield linearly [ P < 0.001; 9.5, 0.5, and 0.1 mL CH₄/g feed DM (SEM = 1.1) for 0.25, 0.5, and 1.0% CHBr₃, respectively]. I n Exp. 1, daily CH₄ emission decreased linearly (P < 0.001) with AT inclusion rate: 392, 367, 84, and 83 g/d, (SEM = 20) for BG, 0.25, 0.5, and 0.75% AT,  respectively. Methane yield was decreased quadratically (P = 0.02; from 17.5 to 5.7 g/kg DMI; SEM = 1.3) by AT. DMI and MY were decreased (P ≤ 0.05) by  15 to  22 % at  the highest (0.75%)  AT inclusion level.   In Exp. 2 , daily CH₄ emission decreased ( P  < 0.001) by 35 %  at the 0.50% AT inclusion  rate  compared with  the control, 351 vs. 229 g/d (SEM = 19.4). Methane yield was also decreased ( P < 0.001) by 29% at the 0.50% AT inclusion level . Dry matter intake and MY were  decreased ( P = 0.00 6)  by 6.9% and 5.7%, respectively, in cows fed 0.50% AT. The CH₄ mitigation effect of AT appeared to diminish from experimental period 1 (339 vs. 128 g CH₄/d, control and AT, respectively ;  SEM = 29.5 ;  P < 0.001)  to experimental period 4 (299 vs. 337 g CH₄/d, control and AT, respectively ; SEM = 29.5 ; P = 0.35) of the study. Oregano leaves and AT at  0.25% had no effect on enteric CH₄ emission in Exp. 2. Aparagopsis taxiformis has the potential to decrease enteric CH₄ emission in lactating dairy cattle ; however, further research needs to determine  the persistency of the mitigation effect of AT.