[Various blood parameters of energy metabolism in dairy cows at the start of lactation].

Thirty eight lactating dairy cows were given ad libitum a diet of maize silage supplemented with concentrate (3 to 5.5 kg/day). Five blood samples were taken from 25 cows from the last week of pregnancy to the 8th week of lactation. The other thirteen cows were subjected to a more frequent sampling (three times a week during the first five weeks of lactation). Each plasma sample was analyzed in order to assess its glucose, acetone, beta-hydroxybutyrate and non-esterified fatty acids contents. The glucose content of the plasma was minimum and the acetone content was maximum at the end of the second week of lactation when the cumulated energy balance was at its most negative level. It appeared that the individual glucose and acetone contents were closely related to the cumulated energy balance, while the non esterified fatty acids content was closely related to the energy balance at the time of sampling. From all the data obtained, a good negative curvilinear relation between the glucose content and the ketone bodies content was observed. These results are discussed with the mobilization of body reserves during the early lactation and its consequences.