Synergistic effect of organic chromium or selenium on post-absorptive glucose metabolism and blood plasma antioxidant status in Mehraban rams

Rams usually experience summer heat stress. In addition, rams due to high sexual activity during joining season experience doubled stress. Following the stress, the production of free radicals increases and oxidative stress related damages occur. High levels of free radicals cause sperm viability reduction, infertility and alter post-absorptive carbohydrate metabolism and glucose tolerance. There are various strategies to reduce the harmful effects of oxidative stress. The supplementation of antioxidants and some trace elements are important nutritional strategies have been recommended to combat harmful effects of oxidative stress. Therefore, the aim of this study was to investigate the synergistic effect of organic chromium or selenium on post-absorptive glucose metabolism and blood plasma antioxidant status in Mehraban rams.

Sixteen Mehraban rams (2-4 years old, with a body score of 2.5-3.5 and 70.14 kg in initial body weight) were randomly divided in to four groups (n=4). Treatments included two levels of Se 0 and 0.6 mg/ram/day (in form of yeast selenium) and, two levels of Cr, 0 and 1 mg/ram/day (in form of Cr-Methionine). The experiment lasted for 60 days. The supplements were fed daily and with the morning meal and total antioxidant capacity and malondyaldehyde levels were determined at days 30 and 60 of experiment. At the end of the experiment an intravenous glucose tolerance test was performed. To do this, 0.5 g of glucose/kg BW as sterile 50 % dextrose solution (w/v) was infused by jugular vein and subsequently blood glucose concentrations were determined at 5, 10, 15, 20, 25, 30, 45, 60, 90, 120, 150, and 180 min post-infusion. Then plasma glucose kinetics was calculated.

Time effect and treatment×time interaction did not impact malondialdehyde level and total antioxidant capacity. Interaction of chromium × selenium did impact total antioxidant capacity (P < 0.05) but, did not affect malondialdehyde level. Total antioxidant capacity was higher and malondialdehyde level was lower in chromium and selenium groups compared to control. Glucose basal and peak concentrations and amount of change (peak-basal concentrations) after glucose tolerance test did not differ among groups. Glucose concentrations were lower in chromium and selenium co-supplemented compared to chromium or selenium supplemented group at 15, 150 and 180 min glucose post-infusion and a significant chromium × selenium interaction was found (P < 0.05). Interaction of chromium × selenium did not impact glucose concentration at 20, 25 and 120 min post-infusion but glucose concentration at the mentioned time points in 1 mg level showed tendency to decrease compared to 0 levels. Plasma glucose clearance rate at 5 to 15 min post-infusion was higher and half-life was lower in chromium and selenium co-supplemented compared to selenium-supplemented group (P < 0.05). Main effect of chromium at the mentioned time interval was significant and 1 mg Cr/day had higher glucose clearance rate and lower half life (P < 0.05). Area under the curve at 5 to 15 min post-infusion did not differ between groups. Regardless of whether area under the curve was calculated from 0 to 30 min or 0 to 45 min, area under the curve was lower for chromium co-supplemented group compared to Se-supplemented group (P < 0.05).

Results of this study showed that organic chromium and selenium supplements alone or their combination improve the antioxidant status of rams in summer but, only the use of chromium alone or combined with selenium improves the post-absorption glucose metabolism characteristics. Also, the combined use of those two elements does not have a synergistic effect on post-absorptive glucose metabolism and blood plasma antioxidant status in Mehraban rams.