The aim of the studies was to compare lean and obese high-producing milk Holstein-Fresian cows in terms of their insulin sensitivity. 17 animals, 2-8 years of age, weighing 480-725 kg, with a daily milk yield fluctuating between 25.4 and 46.5 kg, were divided into two groups, depending on the body weight and condition: lean and obese cows. Subsequently, both groups were divided into subgroups according to the month of lactation. Their condition was evaluated on a five-point Body Condition Score (BCS) scale. Throughout the entire experiment, the cows were fed ad libitum with the same feed and had free access to fresh water. Blood samples were collected every week directly after milking from the subcutaneous abdominal vein. In the whole blood the glucose level was measured, whereas in the plasma, insulin and FFA concentrations were analysed. On the basis of the results obtained, insulin sensitivity was analysed according to the RQUICKI formula (“Revised Quantitative Insulin Sensitivity Check Index”), and the energy balance was calculated. In both experimental groups of lactating cows, the plasma insulin level was found to be several times higher than the physiological norm for non-lactating animals. The highest insulin concentration was noted in obese cows with BCS 3.5. Moreover, in the obese group a high negative correlation (r = -0.62) between insulin sensitivity and BCS, and a positive correlation between the insulin level and BCS were found. The level of free fatty acids (FFA) increased during the lactation, and in both groups it was higher than the reference data. The highest FFA concentration, similarly to insulin, was found in obese cows with BCS 3.5. The glucose level increased during the lactation in both groups of animals, but it was lower than the physiological norm for non-lactating cows. According to our results, there is a relationship between the insulin concentration, insulin sensitivity, and body condition (BCS) in high-producing milk cows. In high-yielding dairy cows elevated levels of FFA may indicate that insulin sensitivity is suppressed. The fat high-producing cows maintained on a positive energy balance are more likely to develop insulin resistance and succumb to production diseases. The RQUICKI test enables an easy assessment of tissue response to insulin.
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