An experiment was conducted to study effects of abomasal infusions of casein, glucose or starch on milk production and blood metabolites in dairy cows. Four lactating cows (559±41.9kg) fitted with 100 mm ruminal cannulas were used in a 4 × 4 Latin square experiment. The cows were given access ad libitum to grass silage and received 6.2 kg dry matter (DM) of a mixture of rapeseed meal (5.3kg/d DM) and barley grain (0.9kg/d DM) as a basal diet (CON), the basal diet plus intra-abomasal infusions of 270 g sodium caseinate (CAS), 300 g of glucose (GLU) or 243 g of starch (STA) starting at 09:00 h each day. Abomasal infusion of different nutrients did not affect (p>0.05) grass silage intake and rumen fermentation parameters (rumen pH, ammonia N and volatile fatty acids). As unexpected, milk yield and composition data did not differ between CON and the treated groups (p>0.05). Most of plasma amino acids were not significantly (p>0.05) affected by the abomasal infusions of CAS, GLU or STA except for histidine, tryptophan and glycine. Although histidine, known as the first limiting amino acid in dairy cows fed grass silage based diets, was significantly (p=0.003) increased by CAS, we failed to result in a clear increase in milk yield and protein yield. This discrepancy between plasma AA profiles and milk production could be presumably explained by relatively high concentration of total amino acids in the present study (2,039μmol/l).

• Chang W. Choi(Department of Animal Resources, International Research Center for Eradication of Poverty and Hunger, Daegu University)
• K. H. Kim(National Institute of Animal Science, RDA)
• S. H. Choi(Department of Animal Science, Chungbuk National University)