Abstract The objective was to evaluate the effects of microalgae and algal mineral content compared with conventional feedstuffs using an in vitro ruminal fermentation. The experiment was a completely randomized design that included six treatment groups, each using a triplicate of flasks. Each flask contained 7% of the treatment, 37% alfalfa hay and 56% corn silage on an organic matter basis. Treatments included soybean meal (SBM), dried distillers grains (DDG), Tetraselmis algae (TETR), and Thalassiosira algae (THAL). Two additional treatments included 0.4 g of ash from TETR and THAL added to flasks containing the 7% distillers (DDG-TETRash, DDG-THALash). Ash was used to evaluate the effects of mineral content on ruminal fermentation in contrast to the effects of organic matter. Ruminal contents were collected from a beef steer on a silage-based diet. Each flask contained 150mL of rumen fluid mixture (2 McDougall’s buffer:1 rumen fluid ratio). Each flask contained four F57 sealed Ankom bags filled with 0.26 grams DM (1 alfalfa hay:1 corn silage) to determine neutral detergent fiber disappearance (NDFD). Flasks were incubated at 39 °C for 24 h with sample aliquots collected at h 0, 4, 8, 12 and 24 to determine pH. Additionally, volatile fatty acid (VFA), ammonia (NH3), and gas samples were collected at h 0, 8, and 24. Data were analyzed using the MIXED procedure of SAS 9.4. The VFA, pH, and NH3 were analyzed with the effects of treatment, time, and their interactions, while NDFD was analyzed with the effects of treatment. Treatment tended (P = 0.06) to affect gas volume, with SBM having the greatest and DDG-TETRash the least. A treatment by time interaction (P = 0.02) was observed for total VFA concentration. The greatest difference was seen at 24 h with DDG-TETRash (117.37 mMol) being the greatest and SBM (97.93 mMol) being the least. A treatment by time interaction was observed (P 0.01) for acetate, propionate, and butyrate. Acetate and propionate peaked at 8 h with acetate concentrations being the greatest in DDG and SBM, while the greatest concentration for propionate was DDG-TETRash. Butyrate concentrations peaked at 24 h with TETR and THAL being the greatest. Treatment affected NDFD (P = 0.01) with DDG-TETRash (35.43%) being the greatest and DDG-THALash (20.19%) the least. A treatment by time interaction (P 0.01) was observed for NH3. At 8 h TETR (0.88 mg/dL) was greater than DDG-TETRash (0.48 mg/dL). There was a time interaction observed (P 0.01) as pH peaked at 4 h and then decreased over time. Microalgae and algal mineral content both improved some measures of ruminal fermentation during a 24 h in vitro fermentation.
Bruhn et al. (2026) studied this question.