Table 4.

Studies investigating effects on rumen microbiomes after addition of seaweeds/bioactive compounds as feed additives

Seaweeds/ compounds added	Animal	Type of study	Basal diet	Dosage rate	Effects on microbiome	Effect on CH4 emissions	References
Bromochloromethane	Murciano-Granadina lactating goats	In vivo: BCM administered 2 equal doses per day from parturition to 2 weeks postweaning	Alfalfa hay with 600 g/d concentrates	0.3 g of BCM/100 kg body weight	No effect on overall abundance of microbial populations	33% reduction in CH4	[29]
Bromochloromethane	Brahman-crossbred steers	In vivo: 97 d trial- for first 63 d 100 g cotton seed meal was added to basal diet and for 34 d BCM added to the cotton seed meal	Rhodes grass and grain pellets	0.3 g of BCM/100 kg body weight	Decrease in Methanobrevivacter spp. observed when treated with BCM 34% average decrease in methanogenic archaea	30% reduction in CH4 emissions	[31]
Bromochloromethane	Non-lactating Friesian-Holstein cattle	In vitro: Batch and continuous fermentation tested	Batch: hay Continuous: 20 g/d hay	Batch: 5 µmol/L and 10 µmol/L tested Continuous: 5 µmol/L	Batch fermentation: 48% decrease in Ruminococcus flavefaciens, 68% increase in Fibrobacter succinogenes and 30% increase in ruminal fungi Continuous fermentation: significant decrease in Ruminococcus flavefaciens and methanogens, no change to Fibrobacter succinogenes population, increase in rumen fungi	Batch: 89%–94% reduction of CH4 at both concentrations tested Continuous fermentation resulted in 85%–90% CH4 reduction	[75]
Asparagopsis taxiformis Bromoform	Brahman steers cattle	In vitro: batch fermentation	Rhodes grass	2% of organic matter 2 concentrations tested: 1µmol/L and 5µmol/L	Decrease in CH4 production correlated with a decrease in relative abundance of methanogens; particularly Methanobacteriales, Methanomassiliicoccales, Methanomicrobiales.	> 99% reduction compared to basal substrate only control Addition of 1 µmol/L reduced CH4 by 77% and 5 µmol/L reduced CH4 by > 99% compared to basal substrate-only control	[13]
Bromochloromethane	Japanese native (Shiba) goats	In vivo: animals sequentially adapted to low, medium, and high doses of BCM	50% timothy grass 50% concentrates	Low dose: 0.5 g/100 kg live weight Medium dose: 2 g/100 kg live weight High dose: 5 g/100 kg live weight	Decrease in abundance of methanogens and fungi, and decrease in Ruminococcus albus Increases in Prevotella spp. and Fibrobacter succinogenes No change to Ruminococcus flavefaciens or protozoa	Low dose: 5% reduction in CH4 Medium dose: 71% reduction in CH4 High dose: 91% reduction in CH4	[76]
Asparagopsis taxiformis	Angus-Hereford beef steers	In vitro: RUSITEC	Super basic ration containing 70% alfalfa pellets, 15% rolled corn, 15% dried distillers grains	5% w/w	Decrease in relative abundance of methanogens compared to the control; decrease was significant when averaged over the course of the experiment	95% reduction in CH4 formation	[45]
Phlorotannins extracted from Ascophyllum nodosum	Steers	In vitro: batch fermentation	Mixed forage (50:25:25 ground barley silage:alfalfa hay:grass hay)	500 µg/mL phlorotannin extract Extract determined to contain 220 mg phlorotannin/g dry matter	At 500 µg/mL phlorotannin addition, growth of Fibrobacter succinogenes reduced by 78% at 6 h, 83% at 12 h, and 65% at 24 h No effect on Ruminococcus flavefaciens Ruminobacter amylophilus, Prevotella bryantii, Selenomonas ruminantium were increased at 12 and 24 h	Not analysed in this study	[66]
Undaria pinnatifida Sargassum fusiforme Sargassum fulvellum	Non-lactating Hanwoo cows	In vitro batch fermentation	300 mg timothy hay 200 mg corn grain	0.25 mg/mL	Sargassum fusiforme increased the overall abundance of total bacteria, ciliate protozoa, fungi, methanogenic archaea, Fibrobacter succinogenes. Relative proportions of Butyrivibrio fibrisolvens, Butyrivibrio proteoclasticus, and Prevotella ruminicola decreased with addition of seaweeds	Undaria pinnatifida reduced CH4 emission by 26.8% at 12 h and 21.3% at 24 h Sargassum fusiforme reduced CH4 emission by 23.4% at 12 h and 24.4% at 24 h Sargassum fulvellum reduced CH4 emission by 26.3% at 12 h and 24.6% at 24 h	[50]
Ecklonia stolonifera Eisenia bicyclis Sargassum fulvellum Undaria pinnatifida Sargassum fusiforme	Holstein cows	In vitro batch fermentation	Timothy grass	5% dry matter basis	At 12 and 24 h, the abundance of methanogenic archaea decreased in the presence of Ecklonia stolonifera, Eisenia bicyclis and Sargassum fulvellum At 12 and 24 h, the abundance of methanogenic archaea increased in the presence of Undaria pinnatifida and Sargassum fusiforme	For all seaweeds except Sargassum fusiforme, CH4 emission increased at 6 and 24 h incubation After 48 h, CH4 was reduced by: 36.1% for Ecklonia stolonifera 32.4% for Eisenia bicyclis 10.4% for Sargassum fulvellum 26.7% for Undaria pinnatifida 13.9% for Sargassum fusiforme	[51]