Quercetin has been shown to be a potent
antioxidant, acts hepatoprotectively, and affects
glucose and lipid metabolism in monogastrics. If this is also true in ruminants,
quercetin could be beneficial in periparturient high-yielding dairy cows by ameliorating the negative effects of
free radical formation and reducing the severity of liver
lipidosis and
ketosis. In a first attempt to evaluate effects of a long-term
quercetin treatment, we intraduodenally administered twice daily 18 mg of
quercetin (Q)/kg of
body weight to 5 late-lactation (215d in milk) dairy cows over a period of 28 d. Frequent blood samples were taken before and during administration to determine plasma concentrations of
flavonols and metabolites. Before and after 1 and 4 wk of Q administration,
glycogen and fat content as well as
mRNA expression of selected genes were measured in liver biopsies. Furthermore, euglycemic, hyperinsulinemic, and hyperglycemic clamp studies were conducted before and after 2 wk of Q administration. During the experiment, dry matter intake and most other zootechnical data remained unchanged.
Milk protein content was increased in wk 2 and 4 of Q administration compared with basal values, whereas fat and
lactose contents of milk remained unchanged. Plasma
nonesterified fatty acids, γ-glutamyl
transferase,
cholesterol,
glutamate dehydrogenase,
triglyceride, and
albumin concentrations, as well as liver fat and
glycogen concentrations, were not affected by Q supplementation. Plasma
glucose and β-hydroxybutyrate concentrations in plasma decreased and increased, respectively, under the influence of
quercetin. During hyperglycemic clamp conditions, the relative increase of plasma
insulin was higher after 2 wk of Q administration, and a tendency for an increased rQUICKI (revised quantitative
insulin sensitivity check index) was observed. The relative
mRNA expression levels of selected genes related to
glucose metabolism, fat metabolism, and antioxidative status were not altered after 1 or 4 wk of Q supplementation. In conclusion, the effects on
insulin release and sensitivity support the assumption that administration of Q could have positive effects on the metabolic adaption of high-yielding cows to early lactation. The increase of
milk protein content in response to Q supplementation needs to be verified.