[Relation between milk production and biochemical indicators in high- and low-producing cows]

23 cows of the Holstein-Friesian breed during second lactation were used in the experiment. All animals were housed in one stable with tying. The blood was collected from each cow four times during first to third, fourth to sixth, seventh to ninth and above nine months of lactation. After 305 days of lactation, the milk cows were classified as with high (n = 14) and lower performance (n = 9), the limit value was 5000 kg of milk. The difference in milk production between groups was highly significant even during the period of the first 90 days (501 kg) and this difference increased for 305 days of lactation to 1538 kg (Tab. I); the dairy cows with high performance produced 6162 kg of milk per 305 days and that with the lower performance gave 4624 kg during the same period. Another significant differences occurred in the fat contents per kg and in the amount of milk converted on 4% fat content. During the first stage of lactation a slightly higher haemoglobine level was found in cows with high performance, the opposing results were obtained in another studies (Tab. II), the highest difference was recorded in the course of 7th to 9th month. The level of total protein was, except 7th to 9th month, always higher in cows of the first group. The difference was significant at the beginning of lactation. Insulin concentration (INS) exhibited identical tendency for the whole lactation--dairy cows with high milk production exhibited lower values, significant differences were recorded in the first observation at the beginning of lactation and in the period above 9 months. Similarly as in case of insulin, it is also in hormones of thyroid gland, the cows with high milk capacity had the lower values (Tab. III). The highest differences in triiodothyronine (T3) concentration were recorded in the second half of lactation, significance ranged from 7th to 9th month of lactation. In thyroxine content (T4), marked differences were recorded during the first and last observations, the difference was highly statistically significant during the seventh to ninth month of lactation. The levels of cyclic adenosine monophosphate (AMP) were higher for the whole experiment in animals with lower milk production. Tab. IV gives the correlation coefficient of different parameters between periods under study. Almost all parameters are in a close positive relation, the closest dependences were observed between second, third and fourth periods in hormones of thyreoidea. The most significances were recorded in adenosine monophosphate, thus confirming its stability of minimum variance between observations.(ABSTRACT TRUNCATED AT 400 WORDS)