Evaluation of Three Marine Algae on Degradability, In Vitro Gas Production, and CH₄ and CO₂ Emissions by Ruminants

Livestock production systems are responsible for producing ~18% of the total anthropogenic greenhouse gas (GHG) emissions. Numerous alternatives, such as feed additives or supplements, have been proposed to meet these challenges. Marine algae have been proposed for gas reduction in ruminants; nevertheless, there are still very few experimental reports. Thus, the objective of the current study was to identify the volatile organic compounds (VOCs) in three marine algae—Kelp (<i>Macrocystis pyrifera</i>), Ulva (<i>Ulva</i> spp.), and Silk (<i>Mazzaella</i> spp.)—and to test their in vitro ruminal fermentation characteristics, gas profiles, and ability to mitigate biogas production. The evaluation of the VOCs in marine algae was performed using a flash gas chromatography electronic nose (FGC-E-Nose). The in vitro study was elaborated through in vitro incubation and gas production. The data obtained were analyzed using a completely randomized design. In total, forty-three volatile compounds were identified for Kelp algae, thirty-eight were identified for Ulva algae, and thirty-six were identified for Silk algae; the compounds were from different chemical families and included aromas, alcohols, aldehydes, phenolics, carboxylic acids, esters, and nutraceutical properties. Dry matter degradability was significantly (<i>p</i> < 0.05) affected by the algae type. The cumulative ruminal gas production was different (<i>p</i> < 0.05) between treatments. Kelp algae presented a major (V; <i>p</i> < 0.05) volume of gas produced compared to the other algae. Lag time (l; <i>p</i> < 0.05) was increased by Kelp alga; however, there were no differences (p>0.05) between the Silk and Ulva algae. The gas production rate was higher (s; <i>p</i> < 0.05) for Silk algae compared to the others. Ulva and Silk algae demonstrated a significant (<i>p</i> < 0.05) decrease in carbon dioxide emissions. Nevertheless, Kelp algae reduced the proportional methane (CH₄) production (<i>p</i> < 0.05) after 48 h of incubation, with the lowest emission rate of 47.73%. In conclusion, algae have numerous bio compounds that provide some properties for use in ruminant diets as additives to reduce methane and carbon dioxide emissions.