ETIOLOGY OF LIPID-RELATED METABOLIC DISORDERS IN PERIPARTURIENT DAIRY-COWS

Plasma NEFA concentrations increase prior to and at parturition, resul ting in increased fatty acid uptake by the liver, fatty acid esterific ation, and triglyceride storage. Liver triglyceride concentration incr eases four- to fivefold between d 17 prior to calving and d 1 followin g calving. Increases in liver triglyceride following calving do not ap pear to be dramatic. Severity of fatty liver 1 d postpartum is correla ted negatively with feed intake 1 d prepartum. Export of newly synthes ized triglyceride as very low density lipoprotein occurs slowly in rum inants and is a major factor in the development of fatty liver. Nutrit ional strategies to minimize the elevation in plasma NEFA prior to cal ving results in lower liver triglyceride at calving. Fatty liver proba bly precedes clinical spontaneous' ketosis. Liver triglyceride to glyc ogen ratio may be used to predict susceptibility of cows to ketosis. C onsequently, strategies to reduce liver triglyceride at calving may de crease incidence of ketosis. Research to determine methods to reduce f atty acid delivery to the liver or to enhance hepatic export of very l ow density lipoprotein near calving is warranted. Identification of th e cause for the slow rate of assembly and secretion of hepatic very lo w density lipoprotein in ruminants will be required to assess the feas ibility of increasing export of very low density lipoprotein.