Abstract
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.
Highlights
Enteric methane (CH4 ) production is a main target of greenhouse gas mitigation practices in livestock, and several mitigation strategies have been proposed [1]
Cow M1 was euthanized on a decision by the veterinarian on day 13, due to abomasal displacement, probably related to low feed intake and low rumen activity
Cows L1, L3, L6, and H2 continued to receive the seaweed mix from day 14 onwards, and the seaweed mix treatment for cow H2 was stopped at day 16 due to reduced intake
Summary
Enteric methane (CH4 ) production is a main target of greenhouse gas mitigation practices in livestock, and several mitigation strategies have been proposed [1]. CH4 formation in the rumen of sheep [2]. The use of CHBr3 containing seaweeds (i.e., Asparagopsis taxiformis and Asparagopsis armata) to mitigate enteric CH4 emission of cows has gained increasing attention. The red seaweed A. taxiformis effectively reduces CH4 production in in vitro gas production systems [3,4,5], with 99% reduction in CH4 production, and an inclusion rate of 2% organic matter (OM) basis [6]. The underlying mechanism might be related to the reduced efficiency of the cobamide-dependent methyl transferase by interacting with reduced vitamin B12 [8], a crucial step of methanogenesis in the rumen
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