Effects of heat stress and zinc supplementation on swine metabolome

Abstract Text:

Heat stress (HS) greatly affects energy metabolism, but the impact of HS on the swine metabolome is not well characterized. In this study, metabolic effects of HS and Zn supplementation were evaluated using three diets: ZnNeg (no Zn supplementation), ZnIO (120 ppm ZnSO₄), and ZnAA (60 ppm ZnSO₄ + 60 ppm Availa^®Zn zinc amino acid complex). Diets were formulated based on NRC (2012) requirements and fed to crossbred gilts (71 ± 9 kg BW, n = 8/trt). Following a 3 × 2 factorial design, pigs were acclimated to experimental diets for 2 weeks, then challenged with a diurnal HS treatment (12 h at 37°C and 12 h at 25°C per day) or maintained in a thermal-neutral (TN) environment (21°C) for 7 d. Blood samples were collected on days 1, 2, 5, and 7 during HS treatment, while tissue, cecal fluid, and feces were harvested after sacrifice on day 7. The metabolic changes associated with HS and Zn supplementation were evaluated by growth performance, blood chemistry, and untargeted metabolomics. Compared with the TN environment, HS greatly decreased ADG (1.17 vs. 0.44 kg; P < 0.01), ADFI (3.36 vs. 2.06 kg; P < 0.01), and G:F ratio (0.35 vs. 0.20; P < 0.01). However, Zn supplementation did not affect growth performance under either TN or HS conditions. Results from blood chemistry showed that HS and Zn supplementation did not alter serum level of glucose, triglycerides, cholesterol, Fe, and Zn. However, HS led to higher creatinine (1.08 vs. 0.88 mg/dL; P < 0.01) and lower BUN (12.79 vs. 16.06 mg/dL; P < 0.01) serum level versus TN. This was likely caused by elevated muscle degradation and reduced renal reabsorption in HS. Untargeted metabolomic analysis of serum, liver, fecal, and cecal extracts revealed clear separations of HS and TN samples in the multivariate models, suggesting that HS greatly affected chemical composition of the metabolome. Subsequent structural and quantitative analyses identified diverse HS-induced changes in amino acid, lipid, and bacterial metabolism, such as the decrease of free lysine in serum (172.47 vs. 249.03 µM; P < 0.01) and increase of acetic acid in cecal fluid (1.69 vs. 1.24 mM; P < 0.01). Overall, metabolomic analysis provided novel and comprehensive information on the metabolic events associated with HS and Zn supplementation, which warrant further investigation into the roles of these metabolic events in growth and stress response.

Keywords: heat stress, metabolomics, zinc supplementation