The effect of different concentrations of microalga Chlorella vulgaris supplementation on ruminal fermentation and blood indices in cows

This study examined the effects of dietary Chlorella vulgaris supplementation on ruminal fermentation, blood biochemistry, and protozoal composition in dairy cows. Four ruminally cannulated Simmental cows (6.00 ± 0.83 years; 521.00 ± 9.51 kg body weight) were assigned to a 4 × 4 Latin square over 72 days. Cows received a basal diet (ALG0) or the same diet supplemented with 2.76 (ALG1), 8.22 (ALG2), or 16.3 (ALG3) g/kg odf dry matter (DM) of lyophilized C. vulgaris . Alga supplementation affected ruminal pH ( P = 0.013), which was highest in ALG2 (6.69) and lowest in ALG3 (6.23). Nitrogenous compounds increased with algae inclusion, with NH 3 -N peaking in ALG2 (8.82 mmol/l; P = 0.001) and total nitrogen highest in ALG3 (5.8 g/kg; P < 0.001). Protozoal counts rose significantly with supplementation ( P = 0.001), especially in ALG3. Volatile fatty acid concentrations and molar proportions were unaffected ( P > 0.10), and the acetate-to-propionate ratio remained stable. Blood biochemical indices were largely unchanged ( P > 0.05). Total protein tended to increase, while glucose showed a non-significant decline at the highest alga dose. Other markers, including 3-hydroxybutyric acid (BHB), nonesterified fatty acids (NEFA) and liver enzymes, remained within physiological limits. These results suggest that C. vulgaris can enhance nitrogen metabolism and protozoal activity without adversely affecting metabolic health, supporting its potential as a functional feed additive in dairy nutrition.