The Effect of Microalga Chlorella vulgaris and Cyanobacteria Spirulina platensis Supplementation on Rumen Fermentation in Cattle

Abstract

Microalgae are a promising protein source for ruminants, yet their in vivo effects on rumen fermentation are variable. We evaluated dietary Chlorella vulgaris (CHL), Spirulina platensis (SPIR), and a 50 : 50 mixture (MIX) in four ruminally cannulated Simmental cows using a 4 × 4 Latin square. Cows received a control diet (CON) or CON supplemented with CHL (100 g/d), SPIR (100 g/d), or MIX (50 g CHL + 50 g SPIR/d). Rumen fluid collected three hours post-feeding was analyzed for pH, volatile fatty acids (VFA), ammonia (NH₃–N), total nitrogen (Ntot), and total protozoal ciliates (TPC). Treatments affected most fermentation endpoints. Relative to CON, CHL lowered pH (6.17 vs. 6.37; P < 0.001) and increased propionate (19.24 vs. 16.78–17.40 mmol/L; P = 0.001), indicating a more glucogenic profile. MIX increased acetate (78.43 vs. 69.02 mmol/L; P = 0.002), the acetate: propionate ratio (4.82 vs. 3.99–4.38; P < 0.001), isovalerate (1.09 vs. 0.75–0.86 mmol/L; P < 0.001), NH₃–N (2.83 vs. 1.69–2.34 mmol/L; P < 0.001), Ntot (0.57 vs. 0.46–0.51 g/kg; P = 0.01), and TPC (35.02 vs. 26.43–29.04 ×10⁴/mL; P = 0.005). SPIR responses were intermediate and generally closer to CON. At practical inclusion rates, C. vulgaris favored propionate production with a modest decline in pH. In contrast, the CHL+SPIR mixture shifted fermentation toward higher acetate, branched-chain VFA, and deamination products, alongside greater protozoal abundance. Thus, single-species versus mixed microalgae should be selected based on production goals: CHL for glucogenic energy supply, and MIX for acetate-oriented fermentation, acknowledging potential impacts on rumen nitrogen efficiency.