Heat stress (HS) adversely impacts all aspects of global agriculture, and it particularly constrains domestic animal productivity and compromises animal welfare. Heat-stressed animals employ physiologic and metabolic adjustments to ameliorate the heat insult; consequently, efficiency is compromised because nutrients are partly diverted away from production purposes to maintain euthermia. Reduced animal productivity during HS can also be attributed to the direct effects of HS (independent of nutrient intake) on metabolism, physiology, reproduction, and health. Therefore, identifying nutritional alternatives with the potential to ameliorate the detrimental effects of HS on economically important performance and health is of particular interest. The overall thesis objectives were to investigate the dietary effects of chromium (Cr) and zinc (Zn) supplementation in heat-stressed and nutrient-restricted pigs.

In the first study (Chapter 2), finishing pigs were used in a replicated experiment to evaluate the effects of Cr propionate supplementation on growth performance and metabolism during HS. As expected, pigs exposed to HS had increased thermal indices and decreased growth performance. However, Cr supplementation tended to increase average daily gain in chronically heat-stressed pigs. Regardless of environmental treatments, pigs supplemented with Cr had numerically increased feed intake. Further, adding Cr to the HS pig diet increased circulating neutrophils and monocytes.

The second study (Chapter 3) evaluated the effects of Zn amino acid complex on metabolism, leaky gut biomarkers, and inflammation during and following HS. Pigs exposed to HS had increased body temperature and respiration rates as well as reduced production metrics. Despite marked reductions in feed intake, circulating insulin increased during HS and remained increased during thermal neutral recovery. Interestingly, supplemental Zn tended to decrease plasma tumor necrosis factor alpha (TNFα) levels before and after HS exposure. However, no effects of dietary Zn were observed on production parameters or other blood metabolites.

In conclusion, both experiments demonstrated that HS adversely impacts animal productivity and health. Results suggest that Cr supplementation might be beneficial on growth performance and health during HS. Additionally, Zn supplementation might be advantageous at reducing basal inflammation. Altogether, these findings suggest that dietary interventions aimed at alleviating the negative consequences of HS are plausible. However, additional research is needed to better understand the biology and mode of action of both Cr and Zn supplementation during HS.