| Summary: | Enteric methane (CH<sub>4</sub>) is the main source of greenhouse gas emissions from ruminants. The red seaweeds <i>Asparagopsis taxiformis</i> (AT) and <i>Asparagopsis armata </i>contain halogenated compounds, including bromoform (CHBr<sub>3</sub>), which may strongly decrease enteric CH<sub>4</sub> 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 CHBr<sub>3</sub> 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 CHBr<sub>3</sub> to the urine at days 1 and 10 (10–148 µg/L) was found with all treatments. On day 1, CHBr<sub>3</sub> 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, CHBr<sub>3</sub> does not accumulate in animal tissue, but can be excreted in urine and milk.
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