Table 1.

In vitro studies incorporating whole macroalgal biomass in ruminant feed and effects on CH₄ emission

Seaweed species	Animal	In vitro system	Basal diet	Inclusion rate	Impact on CH4 emissions	References
Red seaweeds
Asparagopsis taxiformis	Holstein cows	Ankom gas production system	70% alfalfa 15% dried distillers grain 15% rolled corn	5% dry matter	Reduction of 74% CH4 in comparison with control	[38]
Asparagopsis taxiformis	Lactating Swedish Red cows	Gas production recorder	Timothy grass, rolled barley, rapeseed in ratio 545:363:92 g/kg diet dry matter	20 g/kg organic matter 0 g/kg 0.06 g/kg 0.13 g/kg 0.25 g/kg 0.5 g/kg 1.0 g/kg diet organic matter	99% CH4 inhibition compared to control, when included at 20 g/kg organic matter Dose dependent response observed with CH4 emission decreasing curvilinearly	[39]
Mastocarpus stellatus  Palmaria palmata  Porphyra sp.	Murciano-Granadina goats	Batch fermentation	1:1 oat hay and concentrate (containing cereals at 633 g/kg fresh matter)	84 g/kg fresh matter 130 g/kg fresh matter 150 g/kg fresh matter	No statistically significant reduction in CH4 emission observed	[19]
Halymenia floresii  Hypnea pannosa	Brahman steers cattle	Ankom gas production system	Rhodes grass	20% organic matter	No statistically significant reduction in CH4 emission observed	[18]
Asparagopsis taxiformis	Brahman steers cattle	Ankom gas production system	Rhodes grass	0.5%–10% organic matter	Dose dependent response observed with total inhibition of CH4 at dose rates ≥ 2%	[40]
Bonnemaisonia hamifera  Euptilota formisissima  Plocamium cirrhosum  Vidalia colensoi	Non-lactating Friesian × Jersey dairy cows	Batch fermentation	Ryegrass hay	0 2% 6% 10% feed organic matter	Bonnemaisonia hamifera reduced CH4 emission by 17.1% at 2% inclusion rate, 95.4% at 6% inclusion rate, and 98% and 10% of inclusion rate Euptilota formisissima and Plocamium cirrhosum when included at 10% reduced CH4 by 50.5% and 39.5% respectively	[41]
Chondrus crispus  Furcellaria spp.	Lactating Holstein cows	Continuous fermentation vessel	Total mixed ration containing timothy grass, alfalfa, cereals supplemented with vitamins and minerals	0.14 g/d	13% reduction in CH4 compared to control 12% reduction in CH4 compared to control	[42]
Asparagopsis taxiformis  Halymenia floresii  Hypnea pannosa  Laurencia filiformis	Brahman steers cattle	Ankom gas production system	Flinders grass	20% w/w total feed	98.9% reduction of CH4 26.6% reduction of CH4 42.5% reduction of CH4 42.5% reduction of CH4	[17]
Asparagopsis taxiformis	Brahman steers cattle	Ankom gas production system	Rhodes grass	0–16.7% organic matter	99% reduction of CH4 at doses ≥ 2%	[43]
Gigartina sp.  Gracilaria vermiculophylla	Non-lactating Holstein cows	Batch fermentation	Incubated with meadow hay and corn silage	25% dry matter	44% CH4 reduction when incubated with meadow hay but not with corn silage 59% CH4 reduction when incubated with meadow hay and 63% with corn silage	[14]
Gracilaria   vermiculophylla	Non-lactating Holstein cows	RUSITEC	Total mixed ration containing 230 g/kg corn silage, 430 g/kg haylage, 150 g/kg wheat straw, 190 g/kg concentrate	25% dry matter	No effect on CH4 emission	[44]
Asparagopsis taxiformis	One Jersey and one Holstein	RUSITEC	Super basic ration containing 70% alfalfa pellets, 15% rolled corn, 15% dried distillers grains	5% w/w	95% reduction in CH4 formation	[45]
Asparagopsis taxiformis	Lactating Holstein cows	Ankom gas production system	Total mixed ration	1% dry matter	98% reduction in CH4 yield	[16]
Asparagopsis taxiformis	Brahman steers cattle	Ankom gas production system	Rhodes grass	2% of organic matter	Post-harvesting processes including rinsing, freezing, drying tested; the frozen then freeze-dried treatment totally inhibited CH4 emission	[46]
Asparagopsis taxiformis	Brahman steers cattle	Batch fermentation	Rhodes grass	2% of organic matter	> 99% reduction in CH4 compared to basal substrate only control	[13]
Palmaria palmata	Swedish Red cows	Batch fermentation	Total mixed ration (grass silage/concentrate ratio 600/400 g/kg dry matter basis)	Silage replaced by: 0 g/g 0.15 g/g 0.3 g/g 0.45 g/g dry matter	No effect on CH4 emission	[47]
Brown seaweeds
Ascophyllum nodosum  Sargassum fulvellum  Ecklonia maxima  Lessonia flavicans  Lessonia nigrescens  Laminaria japonica	Non-lactating cows	Batch fermentation	50:50 grass hay:concentrates	Two inclusion rates tested: As a feed additive each seaweed was added in addition to basal diet, at 20%. As feed where each seaweed replaced 20% of concentrates in basal diet	As feed additive no effect on CH4 was observed As feed CH4 was reduced by 18% in the case of E. maxima and 21% in the case of L. japonica	[48]
Ascophyllum nodosum  Laminaria digitata	Holstein-Friesian cows	RUSITEC	50:50 forage:concentrates	5% dry matter	No effects on CH4 emissions	[49]
Zonaria farlowii	Holstein cow	Ankom gas production system	70% alfalfa 15% dried distillers grain 15% rolled corn	5% dry matter	11% reduction in CH4	[38]
Undaria pinnatifida  Sargassum fusiforme  Sargassum fulvellum	Non-lactating Hanwoo cows	Batch fermentation	300 mg timothy hay 200 mg corn grain	0.25 mg/mL	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	Batch fermentation	Timothy grass	5% dry matter	For all seaweeds except Sargassum fusiforme CH4 emission increased at 6 and 24 h incubation After 48 h, CH4 reduced by 36.1% for Ecklonia stolonifera, 32.4% for Eisenia bicyclis, 10.4% for Sargassum fulvellum, 26.7% for Undaria pinnatifida, and 13.9% for Sargassum fusiforme	[51]
Cystoseira trinodis  Padina australis  Dictyota spp.	Brahman steers cattle	Ankom gas production system	Rhodes grass	20% feed total (diet organic matter)	Cystoseira trinodis significantly reduced CH4 emission	[18]
Cystoseira trinodis  Dictyota bartayresii  Padina australis  Sargassum flavicans	Brahman steers cattle	Ankom gas production system	Rhodes grass	0.5%–10% organic matter	No significant reduction in CH4 observed	[40]
Cystoseira trinodis  Dictyota bartayresii  Hormophysa triquetra  Padina australis  Sargassum flavicans  Colpomenia sinuosa	Brahman steers cattle	Ankom gas production system	Flinders grass	20% w/w total feed	Strongest CH4 inhibition observed from Dictyota bartayresii, inhibiting CH4 by 92.2%	[17]
Laminaria ochroleuca  Saccharina latissima	Non-lactating Holstein cows	Batch fermentation	Incubated with meadow hay and corn silage	25% dry matter	With meadow hay, no change in CH4 emission With corn silage, addition of Laminaria ochroleuca increased CH4 emission	[14]
Saccharina latissima	Non-lactating Holstein cows	RUSITEC	Total mixed ration containing 230 g/kg corn silage, 430 g/kg haylage, 150 g/kg wheat straw, 190 g/kg concentrate	25% dry matter	No effect on CH4 emission	[44]
Sargassum horneri	Holstein cows	Batch fermentation	Total mixed ration containing grain, cereal meal, alfalfa hay	0 0.5% 1% 2% 3% 4% dry matter	CH4 emission was decreased at 24 h after inclusion of S. horneri	[52]
Saccharina latissima  Alaria esculenta	Swedish Red cows	Batch fermentation	Total mixed ration (grass silage/concentrate ratio 600/400 g/kg dry matter basis)	Silage replaced by: 0 0.15 0.3 0.45 g/g dry matter	Reduction in CH4 emission with increasing inclusion of A. esculenta	[47]
Green seaweeds
Caulerpa lentillifera  Caulerpa taxifolia  Cladophora coelothrix  Ulva ohnoi  Cladophora patentiramea  Ulva sp.  Derbesia tenuissima	Brahman steers cattle	Ankom gas production system	Rhodes grass	20% feed total organic matter	No significant change in CH4 emission observed	[18]
Caulerpa taxifolia  Cladophora patentiramea  Ulva ohnoi	Brahman steers cattle	Ankom gas production system	Rhodes grass	0.5%–10% organic matter	No significant change in CH4 emission observed	[40]
Caulerpa taxifolia  Chaetomorpha linum  Cladophora coelothrix  Cladophora patentiramea  Derbesia tenuissima  Ulva sp.  Ulva ohnoi	Brahman steers cattle	Ankom gas production system	Flinders grass	20% w/w total feed	Addition of Derbesia tenuissima increased CH4 emission Addition of Cladophora patentiramea reduced CH4 by 66.3% compared to control	[17]
Ulva sp	Non-lactating Holstein cows	Batch fermentation	Incubated with meadow hay and corn silage	25% dry matter	When incubated with meadow hay CH4 decreased by 55% When incubated with corn silage no reduction observed	[14]
Ulva rigida	Non-lactating Holstein cows	RUSITEC	Total mixed ration containing 230 g/kg corn silage, 430 g/kg haylage, 150 g/kg wheat straw, 190 g/kg concentrate	25% dry matter	No effect on CH4 emission	[44]
Ulva species B (taxonomically unresolved cultivated species)	Non-lactating Friesian × Jersey dairy cows	Batch fermentation	Ryegrass hay	0 2% 6% 10% organic matter	No effect on CH4 emission	[41]
Ulva sp.	Holstein cows	Batch fermentation	Total mixed ration containing grain, cereal meal, alfalfa hay	0 0.5% 1% 2% 3% 4% dry matter	4% inclusion of Ulva sp. reduced CH4 significantly in comparison with control	[52]