In Vitro Studies on Rumen Fermentation and Methanogenesis of Different Microalgae and Their Effects on Acidosis in Dairy Cows

Two in vitro studies were carried out on nonlactating dairy cows. Experiment 1 compared the methanogenesis and rumen fermentation parameters of various microalgae (<i>Spirulina platensis</i>, <i>Chlorella vulgaris</i>, and <i>Schizochytrium</i> spp.) and protein feeds (sunflower meal, soybean meal, and alfalfa hay) with monensin (MON). Rumen fermentation parameters were determined by an in vitro gas production system. Experiment 2 compared the ability of three microalgae to prevent acidosis. They were tested for 6 h against oat straw (100 mg) and MON (12 g/mL) to ameliorate ruminal acidosis caused by the addition of glucose (0.1 g/mL) as a fermentable carbohydrate with rumen fluid. In experiment 1, there were variations in the nutrient content of microalgae and protein sources. The dry matter content of the substrates ranged from 90 to 94%, and the organic matter content ranged from 82 to 88%, with <i>Schizochytrium</i> spp. having the highest. Protein content in algae and protein feeds ranged from 18–62% of dry matter (DM) to 16–48% DM, with <i>S. platensis</i> and <i>C. vulgaris</i> having the highest. The ether extract of <i>Schizochytrium</i> spp. (45.5% DM) was the highest of any substrate. In vitro rumen fermentation revealed that protein feeds increased the cumulative gas production at the highest level while MON caused a decrease. Ruminal pH was found to be higher in MON (6.95) and protein feeds (6.77–6.81) than in algae (6.37–6.50). In addition, in terms of metabolizable energy and digestible organic matter, protein feeds outperformed algae. The MON produced the least amount of methane (CH₄) of any substrate, but <i>Schizochytrium</i> spp. demonstrated potential for CH₄ reduction. In these groups, the decrease in CH₄ production was accompanied by a decrease in total volatile fatty acids, acetate, and the acetate-to-propionate ratio, but an increase in propionate. Experiment 2 revealed MON as the most effective cure for controlling acidosis. However, <i>C. vulgaris</i> and <i>Schizochytrium</i> spp. had an effect on medium culture pH and demonstrated potential for acidosis prevention. This study found that algae can influence ruminal fermentation, have the potential to reduce CH₄ production, and may reduce acidosis incidence rates. These assumptions, however, must be validated through in vivo studies.