Sub-Antarctic Macroalgae as Feed Ingredients for Sustainable Ruminant Production: In Vitro Total Gas and Methane Production

The sustainable meeting of the global quest for ruminant intensification dictates the need to identify alternative, eco-friendly, and safe feed ingredients. In this sense, macroalgae offer a new paradigm in sustainable ruminant feed supply. This study aimed to investigate the potential of sub-Antarctic macroalgae, including <i>Lessonia flavicans</i>, <i>Macrocystis pyrifera</i>, <i>Gigartina skottbergii</i>, and <i>Ulva Lactuca</i>, regarding their chemical composition, in vitro gas production, and CH₄ production. A completely randomized design consisted of a 96 h (h) incubation that included four different species and a control (alfalfa hay) with buffered rumen fluid. In vitro total gas, fermentation characteristics, and CH₄ production were evaluated. The highest and the lowest crude protein (CP) contents were for <i>U. lactuca</i> (185.9 g/kg) and <i>G. skottsbergi</i> (86 g/kg), respectively (<i>p</i> < 0.0001). All macroalage had lower levels of natural detergent fiber (NDF) and acid detergent fiber (ADF) compared to alfalfa hay (<i>p</i> < 0.0001). The highest potential of gas production (b) was for <i>M. pyriphera</i> (162.8 mL gas/g DM), followed by alfalfa (119.3 mL gas/g DM). However, <i>G. skottsbergi</i> and <i>M. pyriphera</i> showed the highest dry matter degradability at 96 h (68.49 and 67.62 mg/100 mg, respectively; <i>p</i> < 0.0001) and microbial crude protein (679.8 and 669.8 mg/g, respectively, <i>p</i> < 0.0001). All four tested algae produced lower amounts of methane compared to alfalfa hay (<i>p</i> < 0.0001). After 24 h of incubation, <i>M. pyriphera</i>, <i>L. flavicons, G. skottsbergi,</i> and <i>U. lactuca</i> reduced CH₄ by 99.7%, 98.6%, 92.9%, and 79.8%, respectively, when compared with the control. Also, all tested algae had lower (<i>p</i> = 0.0001) CH₄ production (ml CH₄/g Dry matter degradability, DMD) than alfalfa hay. The current results suggest that <i>M. pyriphera</i> and <i>L. flavicons</i> are promising feed additives for ruminants with eco-friendly production and acceptable CP content and DMD that could effectively mitigate CH₄ emissions. Overall, these findings suggest that macroalgae hold promise as a substitute feed source for sustaining ruminant production at the onset of global warming.