Daily changes of blood insulin and plasma energy indices in early lactating cows fed with Total Mixed Ration

Daily blood changes of insulin and energy indices are poorly investigated in dairy cows fed with Total Mixed Ration (TMR), but it is suggested that their daily variations could affect health, milk performances and perhaps feed efficiency. Furthermore, the effects of stage of lactation and of heavy meals on blood indices can be misleading for the interpretation of their values. To clarify this, blood samples from 13 early lactating cows (52±16 days in milk) were taken in 6 different days at 0 (8:00 a.m.), 2, 5, 7, 11, 19 h respectively, after TMR distribution. Li-heparin plasma was analyzed for glucose, urea, NEFA, BHB, ROM and insulin. Moreover, health status, milk yield and its conductivity, rumination profile, BCS and body activity were monitored. Statistical analysis was carried out by repeated measures variance test. After TMR distribution and for 5-7 h, glucose and NEFA decreased, while insulin, urea and BHB increased. Then all the parameters gradually tended to return to pre-TMR administration values. This last situation has been reached during the night and was not modified by the night milking and related small meal. Only NEFA level remained lower at 19 h (vs 0 h) bleeding, suggesting an important raise in early morning only. Plasma urea pattern of change appeared very similar to that of tied cows fed with forage meals mainly during light time. This last result suggests that cows fed with TMR could have some meals in few hours following TMR distribution (8-9 h, till the afternoon milking operation end), but only small meals during the night. With respect to the stage of lactation effect, very fresh cows (36 vs 50 and 68 days in milk) showed the lowest levels of insulin and the highest ones of NEFA at 0 time. Moreover, the same cows showed a smaller rise of insulin and urea after meal. Altogether the results suggest that there is a strong interaction between stage of lactation, time of major meals and time of bleeding on the levels of several blood metabolites and hormones. This means that for a proper comparison of some blood parameters are important both a well standardized protocol of bleeding but also to pay attention to lactation stage and time from TMR distribution.