Body composition of dairy cows according to lactation stage, somatotropin treatment, and concentrate supplementation.

Body weight, condition score, deuteriated water dilution space, estimated body lipids and proteins, and calculated energy and protein balances were determined in 24 multiparous Holstein cows at wk 1, 7, 20, and 39 after parturition. Cows received two levels of energy concentrate (high and low groups) from wk 3. The objective was to estimate changes in body composition as affected by stage of lactation, concentrate level, and bST administration or placebo from wk 9 in a 2 x 2 factorial design. Cows from high and low energy groups lost 25 and 35 kg of body lipids and 3.3 and .5 kg of body proteins, respectively, during the first 7 wk of lactation. During the end of the winter period (wk 8 to 20), control and bST-injected cows lost 8.5 and 21.1 kg of body lipids, respectively. During the grazing period (wk 20 to 39), bST-injected cows gained more BW (34 kg), water (36 kg), and estimated proteins (5.8 kg) and lost more condition score (-.2 units) and estimated lipids (-11.5 kg) than controls. Using data from control periods, it was calculated that 1 unit change in body condition score corresponded to changes of 35 to 44 kg in BW (corrected for estimated gut content variation), 21 to 29 kg in body lipids, and 200 to 300 Mcal in body energy. One kilogram of corrected BW change corresponded to a change of 4.3 or 5.5 to 5.9 Mcal in body energy when calculated from cumulative energy balances or body components, respectively.

[Automated micro-determination of bovine plasma 3-hydroxybutyrate without deproteinization]. / Micro-dosage automatisé sans déprotéinisation du 3-hydroxybutyrate plasmatique chez les bovins.

An automated method for the determination of plasma 3-hydroxybutyrate (3-HB) is described. The enzymatic principle of Williamson and Mellanby is applied to a discrete computerized analyzer (Isamat, Isa-Biologie, 94230 Cachan, France). Using this method, a single operator can determine each day the 3-HB content of 500-600 bovine plasma samples, without perchloric acid precipitation and without adding hydrazine. Aceto-acetate and acetone don't interfere in 3-HB determination. Addition of oxalate (5 mM) in Tris buffer abolishes the interference of lactate dehydrogenase (LDH). The method is accurate, with a precision of 2.8%, linear over the range 0.05-8 mM, low in cost because it needs small volumes of reagent, and correlates well with results from standard end-point manual method (common variance between the two methods: 94-98%). The method allows to use plasma 3-HB determination for assessing nutritional state of cow herds after a convenient standardization of sampling.

[Effect of food intake on variations in different plasma constituents at the end of gestation and the start of lactation]. / Influence de la prise alimentaire sur les variations de différents constituants plasmatiques chez la vache en fin de gestation et en début de lactation.

Four dairy cows received a diet mainly constituted of a mixture of 60% maize silage and 40% concentrate, within four weeks before and six weeks after calving. During this period, blood samples were taken from the jugular vein, twice a week, before and two hours after the morning meal. Five plasmatic components were analyzed: glucose, non-esterified fatty acids, beta-hydroxybutyrate, acetate and urea. Prandial variations depend on the physiological stage: the post-feeding decrease in concentration of non-esterified fatty acids is very slight during late pregnancy and important during early lactation; concentration of beta-hydroxybutyrate post-feeding increases during late pregnancy, but not during early lactation. These results are discussed with variations of energy balance and feeding level. The correlations between different plasma components are often higher before feeding than after, especially between non-esterified fatty acids and beta-hydroxybutyrate. The concentration of non-esterified fatty acids is highly correlated with energy balance, except during the last ten days before calving.