Improving insulin sensitivity may reduce impacts of heat stress (HS) in pigs by facilitating heat dissipation. Chromium (Cr) has been reported to improve insulin sensitivity in pigs. Therefore, the aim of this experiment was to investigate whether Cr supplementation can mitigate HS in growing pigs. Thirty-six gilts were randomly assigned to 2 diets containing 0 (control) or 400 ppb Cr. After 14 d the supplemented pigs were allocated to either 8 d thermoneutral (20°C constant; TN) or cyclic HS (35°C, 0900 h to 1700 h) conditions and continued their respective diet (n = 9 per group). Growth performance was recorded during the 14-d supplementation period. The physiological responses to HS were monitored by measuring respiration rate, rectal temperature, blood gas chemistry, and feed intake during thermal exposure. Kinetics of plasma glucose, insulin and NEFA were studied by intravenous glucose tolerance test (IVGTT) on d 8 of thermal treatment. Results showed Cr alleviated the HS-increased rectal temperature (P < 0.05) and respiration rate (P < 0.01) at 1300 h and 1600 h during thermal exposure. However, Cr did not mitigate the reduction in average daily feed intake which was reduced by 35% during HS or the HS-induced respiratory alkalosis. Chromium tended to increase average daily gain (0.86 vs. 0.95 kg, P = 0.070) during the 14-d supplementation under TN conditions before thermal exposure, which might be associated with the potential of Cr in improving overall insulin sensitivity, as evidenced by a reduced insulin resistance index calculated by Homeostatic Model Assessment (HOMA-IR; 0.65 vs. 0.51, P = 0.013) and a tendency of reduced fasting plasma insulin concentration (1.97 vs. 1.67 μU/mL, P = 0.094). Heat stress decreased the acute insulin releasing rate (P = 0.012) and consequently slowed glucose clearance rate (P = 0.035) during IVGTT. Besides, HS enlarged the values of area under the curve of NEFA during IVGTT (P < 0.01), indicating a reduced lipid mobilization. In conclusion, HS reduced insulin response to IVGTT. Chromium supplementation exhibited a potential in improving insulin sensitivity and mitigating HS symptoms in growing pigs.

Selenium (Se) and vitamin E are essential micronutrients for animal health and production. The major function of both Se and vitamin E is to prevent the oxidative damage of biological membranes and they can influence growth, reproduction, immune function, health, and product quality in ruminants. Both Se and vitamin E are important for maintaining low cellular and systemic concentrations of reactive oxygen species and lipid hydroperoxides, to ensure optimum cellular function. Discovery of various selenoproteins and vitamin E-responsive genes has contributed significantly to improving our understanding about multiple functions of Se and vitamin E. There is evidence that these functions extend beyond the classical antioxidant properties to immunomodulation and intracellular cell signalling and gene regulation. Research in recent years has also shown that supranutritional supplementation of Se and vitamin E is required to improve the performance of ruminants under certain stressful conditions such as heat stress and during transition period. Considering the growing awareness among consumers of the benefits of antioxidant-rich food, there is a great opportunity for the livestock industries to focus on producing antioxidant-enriched milk and meat products or functional foods. The present review focuses on the recent developments in understanding multiple functions of Se and vitamin E at the cellular and molecular level and the effects of supranutritional supplementation on ruminant performance. In addition, the paper also articulates the potential opportunities to produce functional foods enriched with antioxidants, and underlines the need for optimum supplementation of these micronutrients for efficient ruminant production.

¼ 0.0066, p ¼ 0.034, 25 nmol/L for FRT, b low ¼ 0.684 (0.075, 1.292); Db ¼ 0.697, p ¼ 0.027 and LMS, b low ¼ 1.703 (0.241, 3.165); Db ¼ 1.802, p ¼ 0.020, and 60 nmol/L for ST, b low ¼ 0.030 (-0.001, 0.061); Db ¼ 0.051, p ¼ 0.038. Conclusions:In middle-aged women, the point at which relationships between 25(OH)D and musculoskeletal outcomes change varies for different outcomes. The current cut-off of 50 nmol/L appears too high for some outcomes but reasonable overall to optimise bone and balance in this population.

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