Effects of Heat Stress and Porcine Reproductive and Respiratory Syndrome Virus on Metabolism

Heat stress and immune challenge are costly issues to the swine industry causing significant loss in production and health including reduced efficiency in muscle accretion and energy utilization. Alterations to metabolism and immune response may participate in these shortcomings. The study objectives were to examine the metabolic profiles and immune status of swine subjected to a dual challenge of thermal stress and porcine reproductive and respiratory syndrome virus (PRRSV). To determine this, pigs were subjected to four treatments: thermo-neutral (22° C; TN), thermo-neutral PRRSV infected (TP), heat stress (HS), and heat stress PRRSV infected (HP), during two experimental phases. The first phase consisted of infecting half the experimental group with PRRSV while the rest remained infection free in thermo-neutral conditions. A second phase further divided infected and non-infected into heated conditions for three days of constant heat (35° C) or TN conditions. Venous blood was collected prior to each phase and before sacrifice to analyze for metabolites. At sacrifice liver and longissimus dorsi skeletal muscle samples were collected for gene expression analysis. Pigs in challenged conditions had increased body temperatures, reduced feed intake, and lighter body weights compared to controls, with greatest detriment to dual challenged pigs. In addition, challenged pigs had increased markers of muscle degradation. In challenged pigs, differences (p<0.05) were observed in the metabolic and cytokine gene expression profiles suggesting heat stress blunts the immune response of viral infection in muscle and liver. In conclusion, heat stress and immune challenge directly and indirectly affect metabolism and cytokine expression and both variables may contribute to decreased growth parameters.