The effect of different forms of chromium on weight changes and glucose and insulin tolerance test of Afshari ewes during the transition period under the influence of heat stress

During pregnancy, especially the period around birth, animals make many metabolic adjustments to support the transition from pregnancy to lactation. Since the last two months of pregnancy (late pregnancy) constitute 75% of fetal growth, therefore, enriching the sheep diet can have positive consequences on the health and general performance of the ewe and lamb. In such conditions, using of management and nutritional strategies will reduce the problems during the transition period and heat stress condition. Under stress condition, the mobilization of glycogen reserves and glucose production occur to produce energy to maintain stability in the body. Chromium is one of the scarce essential minerals that plays an important role in the metabolism of carbohydrates, lipids, proteins and nucleic acids. Chromium is part of the glucose tolerance factor that increases the affinity of insulin receptors to insulin hormone and increases the sensitivity of receptors to insulin.

This experiment was conducted to evaluate the effect of different forms of chromium in ewes during the transition period under the heat stress condition. Forty pregnant Afshari ewes from 42±5 days before the expected lambing were assigned to four treatments with 10 replications in a completely randomized design. Experimental treatments included: 1) basal diet without chromium supplementation (control), 2) basal diet containing three milligrams of inorganic chromium per kg of DM, 3) basal diet containing three milligrams of chromium in the form of chromium-methionine per kg of DM and 4) basal diet containing three milligrams of chromium in the form of chromium nanoparticles per kg of DM.

The results showed that ewes receiving chromium had less weight changes at two, four and six weeks after lambing (P≥0.05). Also, supplementation of different forms of chromium increased the body condition score of ewes at the time and six weeks after lambing (P≥0.05). Ewes receiving chromium-methionine and chromium nanoparticles had better body condition than control and inorganic chromium treatments. There was no significant difference in glucose concentration between the treatments 60 and 90 minutes after intravenous glucose injection. After 60, 90, 120 and 180 minutes after the intravenous injection of glucose, the insulin concentration of the ewes receiving different forms of chromium decreased compared to the control treatment (P≥0.05).

In general, the use of chromium, especially in the form of chromium-methionine and chromium nanoparticles, is recommended during the transition period of ewes under the influence of heat stress.