[Free amino acids in the arterial and venous blood of milk cows with different milk production levels].

The cows with a higher production of milk had a lower content of free amino acids in their arterial blood (the difference was significant for lysine and phenyl alanine), as compared with the cows with a lower milk production level. Similarly, the high-performance cows had a higher content of free amino acids in their venous blood before milking (difference significant to highly significant for lysine, phenyl alanine, leucine, isoleucine, valine, cystine and alanine) and after milking (difference significant for lysine). Aspartic acid was the only amino acid contained at a higher amount in the blood of low-performance cows, the difference being partly significant after milking. The protein percentage was somewhat higher in the blood of less productive cows, particularly in venous blood before milking (insignificantly).