Two experiments were conducted to evaluate the use of a closed system, fermentation apparatus (Daisy II incubator) and determine the effects of a yeast culture (YC) preparation (Saccharomyces cerevisiae) on in vitro microbial populations, diet digestion, and fermentation patterns in horses. In Exp. 1, 4 mature horses were fed a pelleted concentrate and alfalfa cubes in a 50:50 (%, as-fed) ratio. Fecal samples were taken from each horse to form the inoculum and placed in 4 separate incubation vessels. Twenty nylon bags (10 with 0.25 g and 10 with 0.50 g of the total mixed diet) were placed in each vessel, and in vitro fermentation was carried out for 48 h to determine DM, NDF, and ADF digestibility. In Exp. 2, fecal samples were taken from 4 mature horses consuming either a high-concentrate (HC) or high-fiber (HF) diet. Filter bags containing the HC or HF diet were added to the 4 incubation vessels along with their respective inoculums. Yeast culture was added to 2 of the vessels containing the HC or HF diet, whereas the other 2 vessels served as controls. Vessels were incubated as in Exp. 1 with samples taken at 24 and 48 h. Filter bags were used to determine DM, NDF, ADF, and OM digestibility, whereas vessel fluid was analyzed for lactate, ammonia, VFA, and microbial concentrations. Results of Exp. 1 indicated that DM, NDF, and ADF digestibility were greater (P < 0.05), whereas the corresponding CV was lower (P < 0.05) for the 0.25- vs. the 0.50-g sample size. In Exp. 2, YC tended (P = 0.10) to decrease ammonia concentrations in the HF diet and increased (P < 0.05) acetate production in the HC diet when compared with the control. There were no effects of YC on pH, lactate, or the measured microbial populations, as well as DM, NDF, or ADF digestibility. The results did, however, show that in vitro and in vivo DM digestibility estimates were similar within a diet. Data from Exp. 1 indicated that the 0.25-g sample size provides a more accurate estimate of DM digestibility with less variation. Although YC had little, if any, effect in Exp. 2, the results indicated that the Daisy II incubator does provide valid estimates of total tract DM digestibility in the horse. These data provide further evidence that this process would be an effective and practical means of approximating the digestibility of diets with varying concentrate to forage ratios.

ObjectiveUpregulation of uncoupling protein 2 (UCP2) is associated with impaired glucose-stimulated insulin secretion (GSIS), which is thought to be an important contributor to pathological β cell failure in obesity and type 2 diabetes (T2D); however, the physiological function of UCP2 in the β cell remains undefined. It has been suggested, but not yet tested, that UCP2 plays a physiological role in β cells by coordinating insulin secretion capacity with anticipated fluctuating nutrient supply, such that upregulation of UCP2 in the inactive/fasted state inhibits GSIS as a mechanism to prevent hypoglycemia. Therefore, we hypothesized that daily cycles of GSIS capacity are dependent on rhythmic and predictable patterns of Ucp2 gene expression such that low Ucp2 in the active/fed phase promotes maximal GSIS capacity, whereas elevated Ucp2 expression in the inactive/fasted phase supresses GSIS capacity. We further hypothesized that rhythmic Ucp2 expression is required for the maintenance of glucose tolerance over the 24 h cycle.MethodsWe used synchronized MIN6 clonal β cells and isolated mouse islets from wild type (C57BL6) and mice with β cell knockout of Ucp2 (Ucp2-βKO; and respective Ins2-cre controls) to determine the endogenous expression pattern of Ucp2 over 24 h and its impact on GSIS capacity and glucose tolerance over 24 h.ResultsA dynamic pattern of Ucp2 mRNA expression was observed in synchronized MIN6 cells, which showed a reciprocal relationship with GSIS capacity in a time-of-day-specific manner. GSIS capacity was suppressed in islets isolated from wild type and control mice during the light/inactive phase of the daily cycle; a suppression that was dependent on Ucp2 in the β cell and was lost in islets isolated from Ucp2-βKO mice or wild type islets treated with a UCP2 inhibitor. Finally, suppression of GSIS capacity by UCP2 in the light phase was required for the maintenance of normal patterns of glucose tolerance.ConclusionsOur study suggests that Ucp2/UCP2 in the β cell is part of an important, endogenous, metabolic regulator that controls the temporal capacity of GSIS over the course of the day/night cycle, which, in turn, regulates time-of-day glucose tolerance. Targeting Ucp2/UCP2 as a therapeutic in type 2 diabetes or any other metabolic condition must take into account the rhythmic nature of its expression and its impact on glucose tolerance over 24 h, specifically during the inactive/fasted phase.

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