Enteric methane (CH₄) is the main source of greenhouse gas emissions from ruminants. The red seaweeds Asparagopsis taxiformis (AT) and Asparagopsis armata contain halogenated compounds, including bromoform (CHBr₃), which may strongly decrease enteric CH₄ emissions. Bromoform is known to have several toxicological effects in rats and mice and is quickly excreted by the animals. This study investigated the transfer of CHBr₃ present in AT to milk, urine, feces, and animal tissue when incorporated in the diet of dairy cows. Twelve lactating Holstein-Friesian dairy cows were randomly assigned to three treatment groups, representing the target dose (low), 2× target dose (medium), and 5× target dose (high). The adaptation period lasted seven days, and subsequently cows were fed AT for 22 days maximally. The transfer of CHBr₃ to the urine at days 1 and 10 (10–148 µg/L) was found with all treatments. On day 1, CHBr₃ was detected in the milk of most cows in the low and medium treatment groups (9.1 and 11 µg/L, respectively), and detected in the milk of one cow in the high treatment group on day 9 (35 µg/L). Bromoform was not detected in milk and urine at day 17, nor at concentrations above the detection limit in feces and collected animal tissues. Two animals (low) were sacrificed, and their rumen wall showed abnormalities. Upon histological examination, signs of inflammation became visible. Animals regularly refused the feed or distinctively selected against AT. In conclusion, within the confines of the present experiment, CHBr₃ does not accumulate in animal tissue, but can be excreted in urine and milk.

The objective was to determine the long-term effect of 3-nitrooxypropanol (3-NOP) on CH₄ emission and milk production characteristics from dairy cows receiving 3-NOP in their diet for a full year, covering all lactation stages of the dairy cows. Sixty-four late-lactation Holstein Friesian cows (34% primiparous) were blocked in pairs, based on expected calving date, parity, and daily milk yield. The experiment started with an adaptation period of 1 week followed by a covariate period of 3 weeks in which all cows received the same basal diet and baseline measurements were performed. Directly after, cows within a block were randomly allocated to 1 of 2 dietary treatments: a diet containing on average 69.8 mg 3-NOP/kg DM (total ration level, corrected for intake of non-supplemented GreenFeed bait) and a diet containing a placebo. Forage composition as well as forage to concentrate ratio altered with lactation stage (i.e., dry period and early, mid, and late lactation). Diets were provided as a total mixed ration and additional bait was fed in GreenFeed units which were used for emission measurements. Supplementation of 3-NOP did not affect total dry matter intake (DMI), body weight or body condition score, but resulted in a 6.5% increase in the yields of energy-corrected milk and fat- and protein-corrected milk (FPCM). Furthermore, milk fat and protein as well as feed efficiency were increased upon 3-NOP supplementation. Overall, a reduction of 21%, 20%, and 27% was achieved for CH₄ production (g/d), yield (g/kg DMI), and intensity (g/kg FPCM), respectively, upon 3-NOP supplementation. The CH₄ mitigation potential of 3-NOP was affected by the lactation stage dependent diet to which 3-NOP was supplemented. On average, a 16%, 20%, 16%, and 26% reduction in CH₄ yield (g/kg DMI) was achieved upon 3-NOP supplementation for the dry period, and early, mid, and late lactation diet, respectively. The CH₄ mitigation potential of 3-NOP was affected by the length of 3-NOP supplementation within a lactation stage dependent diet and by variation in diet composition within a lactation stage dependent diet as a result of changes in grass and corn silage silos. In conclusion, 3-NOP reduced CH₄ emission from cows receiving 3-NOP for a year, with a positive impact on production characteristics. The CH₄ mitigation potential of 3-NOP was influenced by diet type, diet composition, and nutrition value, and the efficacy of 3-NOP appeared to decline over time but not continuously. Associated with changes in diet composition, increased efficacy of 3-NOP was observed at the start of the trial, at the start of a new lactation, and, importantly, at the end of the trial. These results suggests that diet composition has a large effect on the efficacy of 3-NOP, perhaps even larger than the week of supplementation after first introduction of 3-NOP. Further studies are needed to clarify the long-term effect of 3-NOP on CH₄ emission and to further investigate the effect that variation in diet composition may have on the mitigation potential of 3-NOP.

Seaweeds have been studied for their ability to reduce enteric methane emissions of ruminants when fed as a feed supplement. In vivo research with dairy cattle is mainly limited to the seaweed species Ascophyllum nodosum and Asparagopsis taxiformis, whereas in vitro gas production research covers a broader range of brown, red, and green seaweed species from different regions. The objective of the present study was to determine the effect of Chondrus crispus (Rhodophyta), Saccharina latissima (Phaeophyta), and Fucus serratus (Phaeophyta), 3 common northwest European seaweeds, on enteric methane production and lactational performance of dairy cattle. Sixty-four Holstein-Friesian dairy cattle (16 primiparous, 48 multiparous) averaging (mean ± standard deviation) 91 ± 22.6 d in milk and 35.4 ± 8.13 kg/d fat- and protein-corrected milk yield (FPCM) were randomly assigned to 1 of 4 treatments in a randomized complete block design. Cows were fed a partial mixed ration [54.2% grass silage, 20.8% corn silage, and 25.0% concentrate; dry matter (DM) basis] with additional concentrate bait in the milking parlor and the GreenFeed system (C-Lock Inc.). The 4 treatments consisted of a control diet without seaweed supplement (CON), or CON supplemented with 150 g/d (fresh weight of dried seaweed) of either C. crispus (CC), S. latissima (SL), or a 50/50 mix (DM basis) of F. serratus and S. latissima. Milk yield (28.7 vs. 27.5 kg/d, respectively), fat- and protein-corrected milk (FPCM) yield (31.4 vs. 30.2 kg/d, respectively), milk lactose content (4.57 vs. 4.52%, respectively), and lactose yield (1,308 vs. 1,246 g/d, respectively) increased for SL compared with CON. Milk protein content was lower for SL compared with the other treatments. Milk fat and protein contents; yields of fat, protein, lactose, and FPCM; feed efficiency; milk nitrogen efficiency; and somatic cell count did not differ between CON and the other treatments. Depending on week of experiment, milk urea content was higher for SL compared with CON and CC. No effects were observed of the treatments compared with CON for DM intake, number of visits to the GreenFeed, or gas emission (production, yield, or intensity) of CO₂, CH₄, and H₂. In conclusion, the seaweeds evaluated did not decrease enteric CH₄ emissions and did not negatively affect feed intake and lactational performance of dairy cattle. Milk yield, FPCM yield, milk lactose content, and lactose yield increased, and milk protein content decreased, with S. latissima.

Methane inhibitors in cattle diets are a promising strategy to reduce enteric methane (CH₄) emissions. Bromoform (CHBr₃) is effective but not well understood in terms of mechanism, dose response, and side effects such as reduced feed intake. Studies using CHBr₃-containing seaweed are inadequate to isolate the effect of CHBr₃ from other factors. This study aimed to determine the dose-dependent effects of synthetic CHBr₃, delivered via ruminal infusion, on DMI, enteric gas emissions, temporal patterns of gas emissions, and ruminal fermentation in cattle. Four nonlactating, nonpregnant, rumen-fistulated Holstein-Friesian cows (12 yr of age; 781 ± 33 kg BW; mean ± SD) were randomly assigned to 1 of 4 treatment sequences in a 4 × 4 Latin square design. Treatments consisted of 0 (CNTL), 59 (LOW), 192 (MED), or 592 (HIGH) mg CHBr₃/d infused into the rumen as an aqueous solution via the rumen fistula. The daily CHBr₃ dose was divided into 3 equal infusions every 8 h over a 24-h period (0545, 1345, and 2145 h) for 14 consecutive d during experimental periods, followed by a 7-d washout period. Cows were fed grass hay ad libitum, and additional concentrate was supplied through a GreenFeed (C-Lock Inc.), which was also used for enteric gas measurements. Total DMI did not respond linearly or quadratically to increasing doses of CHBr₃ but was numerically 6.2 kg/d lower for HIGH compared with CNTL. Both CH₄ production (g/d) and yield (g/kg DMI) decreased quadratically with increasing doses of CHBr₃. Conversely, hydrogen (H₂) production (g/d) and yield (g/kg DMI) increased quadratically with increasing dose of CHBr₃. Total VFA concentration did not respond linearly or quadratically to increasing doses of CHBr₃ but was numerically 27.8 mM lower for HIGH compared with CNTL. Molar proportions of propionate, butyrate, valerate, and branched-chain VFA increased quadratically, and the molar proportion of acetate decreased quadratically with increasing dose of CHBr₃. Separate 4-parameter logistic functions were fitted to CH₄ and H₂ production (g/d) over the infusion and washout periods, using data from the HIGH treatment. The decrease in CH₄ production and increase in H₂ production stabilized after 56 and 49 h of CHBr₃ infusions, respectively (defined as the time at which 95% of the asymptotic change in gas production was attained). After cessation of the CHBr₃ infusions, the increase in CH₄ production and decrease in H₂ production stabilized after 117 and 99 h, respectively. In conclusion, synthetic CHBr₃ supplementation reduced enteric CH₄ production in a nonlinear, dose-dependent manner, with minor effects at 59 and 192 mg CHBr₃/d doses, but ~90% reduction at 592 mg CHBr₃/d. The HIGH treatment numerically reduced DMI, indicating a potential trade-off between efficacy and feed intake. Temporal modeling showed that the CH₄-suppressing effect of CHBr₃ infusion at 592 mg/d emerged within 2 to 3 d and reversed more gradually over 4 to 5 d after the last infusion. These findings highlight the importance of both dose and temporal dynamics in evaluating CHBr₃ for CH₄ mitigation in ruminants.