The effects of different levels of sodium caseinate on rumen fermentation pattern, digestibility and microbial protein synthesis of Holstein dairy cows

This study was conducted to investigate the effects of different levels of peptide supplementation on rumen fermentation pattern, digestibility and microbial protein synthesis. Three rumen-cannulated Holstein dairy cows were used in a 3 x 3 Latin square experiment within 21 days period. The ruminal infusion of sodium caseinate (CN) was 0 (control), 50 and 100 g/d. Dry matter intake, milk yield and composition, total tract apparent digestibility of nutrient, rumen parameters and purine derivatives in urine of cows were measured. Results showed that dairy cows received sodium caseinate, had significantly increased microbial protein synthesis, milk fat yield, acetate and branched chain fatty acids concentrations in rumen fluid and fiber digestibility compared with the control treatment (P < 0.05). CN significantly affected the concentrations of rumen ammonia nitrogen (NH3-N), rumen peptide nitrogen (Pep-N) and the ratio of rumen ammonia nitrogen/rumen peptide nitrogen (P < 0.05) and consequently blood urea nitrogen, milk urea nitrogen and urinary urea nitrogen concentrations. However digestibility of dry matter and crude protein did not differ among treatments. In conclusion, if the optimum level of NH3-N/Pep-N was the best compromise among the need for rumen fermentation, microbial protein synthesis and nitrogen excretion through urine in animal, the recommended level from this study would be 0.86 in rumen fluid.