Effects of estradiol-17 beta on the net hepatic extraction of triglyceride in vivo in fed and fasted sheep

Etiology of lipid-related metabolic disorders in periparturient dairy cows

Plasma NEFA concentrations increase prior to and at parturition, resulting in increased fatty acid uptake by the liver, fatty acid esterification, and triglyceride storage. Liver triglyceride concentration increases four- to fivefold between d 17 prior to calving and d 1 following calving. Increases in liver triglyceride following calving do not appear to be dramatic. Severity of fatty liver 1 d postpartum is correlated negatively with feed intake 1 d prepartum. Export of newly synthesized triglyceride as very low density lipoprotein occurs slowly in ruminants and is a major factor in the development of fatty liver. Nutritional strategies to minimize the elevation in plasma NEFA prior to calving results in lower liver triglyceride at calving. Fatty liver probably precedes clinical spontaneous ketosis. Liver triglyceride to glycogen ratio may be used to predict susceptibility of cows to ketosis. Consequently, strategies to reduce liver triglyceride at calving may decrease incidence of ketosis. Research to determine methods to reduce fatty acid delivery to the liver or to enhance hepatic export of very low density lipoprotein near calving is warranted. Identification of the cause for the slow rate of assembly and secretion of hepatic very low density lipoprotein in ruminants will be required to assess the feasibility of increasing export of very low density lipoprotein.

Estrogen induction of fatty liver in dairy cattle

Two trials were conducted to determine if estrogen contributes to development of fatty liver in dairy cattle. During trial 1, eight late lactation, nonpregnant cows were assigned to 0 or 15 mg estradiol-17 beta benzoate/d treatment. Days 1 to 3 of the trial were for baseline measurements, and treatments were given from d 4 to 21; on d 20 and 21 animals were fasted. Short-term feed deprivation resulted in increased plasma FFA concentrations and rapid accumulation of triglyceride into liver tissue obtained by biopsy. During starvation, plasma FFA concentration and liver triglyceride content were lower for cows receiving the estradiol-17 beta treatment relative to cows receiving control treatment. Very low density lipoprotein concentration in blood increased dramatically in three of four animals during estradiol-17 beta administration. Because of the decrease in milk production during estradiol-17 beta treatment, it was not known whether this represented a decrease in very low density lipoprotein clearance from blood or reflected a lipotropic response to estradiol-17 beta. Therefore, a second trial was conducted employing nonlactating cows, and control and estradiol-17 beta-treated animals were pair fed. The trial was 33 d with d 1 to 3 for baseline measurements, and treatments were administered from d 4 to 33. All animals were starved from d 19 to 23. Estradiol-17 beta increased hepatic lipid and triglyceride accumulation and plasma very low density lipoprotein concentration during starvation. Plasma FFA concentration was also increased by estradiol-17 beta during this time; therefore, a direct or indirect effect of estrogen on hepatic lipid metabolism could not be delineated.