LIPID-METABOLISM AND INTAKE BEHAVIOR OF DAIRY-COWS - EFFECTS OF INTRAVENOUS LIPID AND BETA-ADRENERGIC SUPPLEMENTATION

The goal of this experiment was to determine whether modulation of bet a(2)-adrenoceptors influenced DMI of lactating dairy cows. Because sti mulation of these receptors induces mobilization of body fat stores, t he effect of such stimulation on feed intake was compared with the eff ect of an intravenous administration of lipid nutrients. Four treatmen ts were infused intravenously over a 4-h period: 1) a beta(2)-agonist (clenbuterol), 2) a beta-blocker (propranolol), 3) triglyceride emulsi on (lipids), or 4) saline. Two trials were carried out for the same fo ur cows to compare the effects of two expected lipolytic situations. T rial 1 used cows at 60 DIM treated with infusions from 0300 to 0700 h, and trial 2 used cows at 92 DIM treated with infusions from 0800 to 1 200 h. Each trial was composed of three consecutive replications of a 4 x 4 balanced Latin square design with 2-d periods. A complete diet ( 70% maize silage and 30% concentrate) was offered for ad libitum intak e. In both trials, clenbuterol reduced DMI on the day of infusion (-7. 9 and -11.2% for trials 1 and 2, respectively) and on the following da y (-5.1 and -6.3% in trials 1 and 2, respectively). This decrease occu rred some time after the end of infusion. Intravenous lipid supplement ation reduced DMI during infusion in both trials and during the entire day in trial 2. Both clenbuterol and lipids increased plasma NEFA onl y during infusion. Propranolol had no effect on DMI or basal lipolysis . The data demonstrated that stimulating beta(2)-adrenoceptors reduced DMI but in a manner different from that of lipid energy supplementati on.