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CHLÁDEK, G., MÁCHAL, L.: Changes in the relationship between blood plasma glucose concentration and milk production in Czech Pied cows in the course of the year. Acta univ. agric. et silvic. Mendel. Brun., 2004, LII, No. 2, pp. 97-104 Groups of 20 to 23 dairy Czech Pied cows were observed monthly for the period of 12 months (12 test days). The cows in experimental groups were in their early lactation. The mean number of lactation was 2,8, the cows were on average 54.8 days after calving and the mean glucose concentration in blood plasma was 3.93 mmol/l. During the first 100 days of lactation milk yield amounted to 2581 kg with 3.91% fat, 3.48% protein and 4.85% lactose. The coefficients of the correlation between blood plasma glucose and the observed milk production parameters calculated independently for each test day ranged as follows: -0.597 to 0.130 for number of lactation, -0.389 to 0.585 for days after calving, -0.462 to 0.361 for milk yield, -0.201 to 0.526 for milk fat content, -0.385 to 0.632 for milk protein content and -0.600 to 0.469 for milk lactose content. The calculated coefficients of the correlation between blood plasma glucose and milk production parameters did not reveal a clear tendency in the relationships. However, the graphic polynomial expression showed that glucose level had a positive relationship with days after calving and mainly positive relationship with milk protein content; glucose content had a negative relationship with milk yield and number of lactation and a mainly negative relationship with fat content and lactose content. Czech Pied, cattle, cows, milk, protein, fat, lactose, blood plasma, glucose Ročník LII 10 Číslo 2, 2004 97 Chládek and Máchal (2002) closely studied the relationship between blood plasma glucose and milk production in Holstein cows. In the course of one year they monthly observed several experimental groups of cows in early lactation (the first 100 days of lactation). The cows produced daily on average 33.5 kg milk with 4.07% fat, 2.98% protein and glucose concentration in blood plasma was 3.63 mmol/l. Authors concluded that the calculated coefficients of the correlation between blood plasma glucose and milk production parameters did not reveal a clear tendency in the relationships. However, the graphic polynomial expression of the relationships showed the tendency towards a positive relationship between blood plasma glucose and milk yield and a negative relationship between blood plasma glucose and milk fat content. The relationship between blood plasma glucose and milk protein content was positive, too, but less evident. The importance of genetic merit for milk production and reproductive success in dairy cows was analysed by Snijders et al. (2001). Authors found out that high genetic merit cows had a higher milk production and a lower plasma glucose concentration than medium genetic merit cows. 98 G. Chládek, L. Máchal Similarities in the chemical structure of carbohydrates in the diet and glucose in blood plasma suggest their close relationship. Lykos et al. (1997) investigated that relationship. They found out that the highest dietary ruminal degradation rate of total non-structural carbohydrates increased the amount of nutrient digested in the intestine and increased milk production and milk true protein content and yield, however, blood glucose and insulin concentrations were not affected. On the other hand, Dhiman et al. (1991) examined the effect of dietary forage to grain ratio on blood constituents in dairy cows and they found out that an increased percentage of forage in the diet decreased blood glucose concentration and that glucose concentration was low at the beginning of lactation and increased as DMI increased. Milk production parameters and blood plasma glucose concentration in dairy cows during the first 100 days of lactation were presented by Zimmerly and weiss (2001). Their study investigated effects of supplemental dietary biotin on performance of Holstein cows during early lactation. The authors found out that milk production linearly increased with biotin supplementation, but did not affect milk fat and true protein percentages; plasma glucose concentration was not affected either. The effect of long-term infusion of glucose in cows treated with recombinant bovine somatotropin before peak milk yield was examined by Leonard and Block (1997). In their study glucose infusion increased milk yield by 3.1 kg on milk yield level 39.6 kg while serum glucose concentration was 61.9 mg/dl. They also noted that in the group, which underwent glucose infusion, the milk yield was lower probably as a result of low blood glucose which amounted only to 39.4 mg/dl. The relationship between blood plasma glucose and milk yield is complicated due to the time lag between sample collections, as described by Lean et al. (1992). Authors observed that a significant negative relationship between milk yield and glucose on the same day is connected with the loss of glucose (in a form of lactose) in milk. A positive relationship between milk yield and glucose found 12 to 15 days later suggested that an increased milk yield acted as a stimulus to increase serum glucose concentrations later, possibly by stimulating food intake or gluconeogenic mechanisms. In general, glucose (blood sugar) represents a transport form of saccharides (Jagoš, 1985). Lower values of glucose were detected in the following circumstances: the absence of disposable energy in feed ration, a narrow nutrients ratio, an insufficient production of propionic acid in forestomach, ketosis and a severe impairment of liver parenchyma. Increased values were detected in restless animals and in stress situations of organism. As a reference value for glucose level in blood plasma they regarded 3.00 – 3.90 mmol/l. The aim of the study was to describe changes (in the course of the year) in the relationship between blood plasma glucose and milk production in Czech Pied cows during the first 100 day of lactation.