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With birth, calves are confronted with a new, extrauterine environment and have to meet their energy demand autonomously. For this reason, it is essential that not only overall energy intake, but also endogenous glucose production work effectively, because glucose is one of the main energy sources during the first stage of life. With the intake of first colostrum calves ingest not only nutrients, but also a plethora of bioactive factors which support the maturation and development of metabolic processes. Colostrum is further essential to support the naïve immune system of newborn calves during the first weeks of life and to mediate passive immunity. Unfortunately, colostrum supply is often inadequate. To support the health status, flavonoids could play an important role in the upbringing of newborn calves. These are secondary plant metabolites with numerous attributed health-promoting properties. One of the most important flavonoids is quercetin, which is proven to possess antioxidative, anti-inflammatory and antimicrobial capacity and to modulate the intestinal microflora. However, quercetin also interacts with glucose metabolism by inhibiting intestinal carbohydrate absorption and reducing plasma glucose concentrations. For newborn calves, such an effect would be crucial. Therefore, it was the main objective of the present work to investigate the effects of an oral quercetin supplementation on the glucose metabolism of newborn calves, because this knowledge would be the prerequisite to consider the usage of quercetin as a health promoting feed additive in calf rearing.
In the first part of the study, 28 newborn male Holstein Friesian calves were assigned to two dietary groups and fed colostrum or a milk-based formula with same macronutrient composition, but without bioactive factors, during the first two days of life. On d 2 of life, groups were subdivided into control and treatment groups, the latter receiving quercetin aglycone with meals during the first week of life. On d 3, intestinal xylose absorption was probed, on d 7, a tracer study was conducted to investigate the first pass uptake of glucose, and on d 8, a liver biopsy sample was taken and analyzed via PCR. The postabsorptive recovery rate of orally administered xylose and 13C6-labelled glucose in plasma was higher in calves that initially received colostrum, indicating a better intestinal absorption capacity and a lower splanchnic glucose extraction when compared to colostrum-deprived calves. Irrespective of quercetin supplementation, the mRNA abundance of hepatic mitochondrial phosphoenolpyruvate carboxykinase and several plasma metabolites were also reduced in formula-fed calves, pointing to a delayed maturation of metabolic pathways after colostrum deprivation. Although quercetin-fed calves initially showed higher peak concentrations of 13C6-glucose in plasma on d 7, this effect did not last for the following hours.
Based on the finding that an oral quercetin supplementation does not seem to disadvantage the glucose metabolism in newborn calves, the health parameters recorded during the trial were evaluated in the second part of this work. Additionally, plasma samples of the calves were analyzed for concentrations of immunoglobulins, acute-phase proteins, as well as parameters of the antioxidative system. Furthermore, the expression of genes for some proinflammatory cytokines, antioxidative enzymes and acute-phase proteins was analyzed in cDNA samples generated from the liver biopsy tissue. Data indicate that an adequate initial colostrum supply supports neonatal health and prepares the calves very well to cope with the new environment. Colostrum-fed calves showed reduced signs of inflammation and were more vital than calves initially fed formula, further, the metabolic status was improved. In contrast to this, the quercetin supplementation did not induce any detectable health-promoting effects, a finding that underlines that results proven in vitro are not always transferable to the organism as a whole.
In summary, it can be concluded from the present work that an oral quercetin supplemen-tation does not impair the glucose metabolism of newborn dairy calves. However, health-promoting properties cannot be reproduced in vivo, hence quercetin feeding cannot compensate for an inadequate initial colostrum supply.