INFLUENCE OF LASALOCID, CATIONOMYCIN AND FEEDING FREQUENCY ON THE POSTPRANDIAL KINETICS OF SOME PLASMA PARAMETERS IN THE RUMEN VEIN, PORTAL-VEIN AND MESENTERIC-ARTERY OF SHEEP

Two adult sheep, A and B, received successively during three experimen tal periods a forage-based pelleted feed, then the same diet supplemen ted with 33 mg/kg of lasalocid (L) or cationomycin (C). The feed was g iven in either eight (sheep A) or two (sheep B) daily meats. After fou r weeks of adaptation, 11 blood samples were taken through catheters i n the rumen vein (RVA) and the mesenteric artery (MAA) in sheep A and in the rumen vein (RVB) and portal vein (PVB) in sheep B over a 5-hour period after the morning meal. Because of a blockage in the catheter it was not possible to measure the effect of C in MAA. Food intake had no immediate effect on the plasma levels measured: the distribution o f eight daily meals stabilized plasma levels and made it easier to det ermine the effect of the ionophores. This effect varied according to t he sampling site, the animal and the antibiotic, sometimes contradicto rily. All the plasma parameters monitored in RVA were significantly mo dified by either one of the ionophores. A decrease in plasma albumin c oncentration (P<0.05) was observed with L in MAA and with C in RVA and MAA. Aceto-acetate concentration decreased (P<0.05) with L in MAA but increased with L and C in RVB. A decrease in glycaemia and uraemia (P <0.05) was observed with L in MAA, RVA and RVB and with C in RVA. Tota l amino acid concentration decreased (P<0.05) with C in RVA or increas ed (P<0.05) with L in PVB and RVB. These variations in results may be due to different mechanisms of action of L and C on digestion, particu larly in the rumen. While the changes undergone by the ketone bodies i n the blood suggested a decrease in hepatic ketogenesis with L, there was no evidence that the ionophores had a direct postprandial effect.