Evaluation of Porcine Reproductive and Respiratory Syndrome and mitigating impact on nursery pigs

Porcine reproductive and respiratory syndrome (PRRS) virus is an economically significant pathogen in the U.S. swine herd. It induces PRRS disease symptoms such as fever, lethargy, hypophagia and an overall reduction in growth performance. If severe enough in pathogenicity, duration and in combination with secondary pathogens, mortality risk increases. Interestingly, in growing pigs the extent to which hypophagia explains reduced performance and alters nutrient requirements during disease is poorly understood. Further, strategies beyond vaccination technologies to mitigate these symptoms are needed in pig populous areas like the Midwest. Therefore, the overall thesis objective herein was to characterize the impact of PRRS on vitamin and mineral requirements in nursery pigs and identify ways to mitigate disease hypophagia and the febrile response in PRRS. To address the overall objective, two research chapters were conducted using nursery pigs (Chapter 2 and 3). In Chapter 2, PRRS and its associated disease hypophagia impact on growth performance, as well as changes in vitamin and mineral status were assessed. The effects of disease on the febrile response and hair follicle function was also examined. A 10-day study was conducted, and pigs were allotted to one of three treatments: ad libitum fed, PRRS virus inoculated, and pair fed. The pair fed treatment was calorically restricted to mimic the PRRS daily feed intake treatments. We hypothesized that PRRS virus challenge would attenuate growth performance and vitamin and mineral differences would be observed due to hypophagia. We also hypothesized that hair growth would be increased in response to disease. The results from the Chapter 2 research indicate the changes in growth performance during a PRRS challenge can be partially explained by hypophagia and sickness behaviors. Reductions in average daily gain (ADG) and average daily feed intake (ADFI) were observed in the PRRS+ and PF treatments (Chapter 2). We observed an increase in body temperature in the PRRS+ treatment and a decrease in body temperature in the PF treatment as hypophagia has also been shown to attenuate body temperatures. Although results varied, PF and PRRS+ treatments had increased liver vitamin and mineral concentrations of iron, copper, zinc, and vitamin A and E. Changes in hair follicle function were also observed. The PRRS+ treatment had 55% of their hair follicles in the resting phase and the PF treatment had 56% of its hair follicles in the active production stage suggesting a change in hair production during a viral challenge and feed restriction and therefore, the use of nutrients. Multiple pro-inflammatory cytokine concentrations were increased in both the PRRS+ and PF treatment, with the PRRS+ treatment containing the highest concentrations. These changes in vitamin and mineral concentrations, fever, hair growth and cytokine production suggest that nutrient utilization during a heath challenge may be in favor of the immune system. Inflammatory, fever, and proliferation maintenance of immune cell populations require a reallocation of dietary nutrients and could suggest that these nutrients are being diverted away from normal processes such as lean tissue growth. However, reductions in feed intake alone can explain some of these behaviors. To mitigate the effects of the immune response and hypophagia in response to PRRS virus infection, vitamin B12, sodium salicylate and isotonic electrolytes mitigation strategies were investigated in nursery pigs (Chapter 3). We hypothesized that these strategies would alleviate disease symptom severity by increasing feed intake and lowering core body temperature. Surprisingly, vitamin B12, sodium salicylate and isotonic electrolytes did not mitigate symptoms nor improve growth rates in PRRS virus infected pigs. However, these interventions proved to be beneficial in survivability rates as the B12 treatment had 75% survivability and the Isotonic treatment had 50% survivability compared to PRRS+ only showing a 25% probability of survival. These data suggest that due to the immune response and decreased feed intake, a reallocation of nutrients away from productive growth is required. Further mitigation strategies need to be discovered to reduce symptom severity and lessen the impact on growth performance