Impact of Enteric Coronaviruses on Nursery Pigs

摘要

Porcine epidemic diarrhea virus (PEDV) and porcine deltacoronavirus (PDCoV) are both enteric coronaviruses that infect enterocytes. Clinical signs for both viral infections include diarrhea, dehydration, and anorexia. Newborn and suckling pigs experience higher rates of mortality compared with nursery pigs due to less developed gastrointestinal tracts and immune systems; however, there is minimal data on the longitudinal impact of enteric coronavirus infection on growth performance, intestinal function and integrity, and metabolism in older nursery-grower pigs. Therefore, the overall objective of this dissertation was to characterize and understand how enteric health challenges modulate nursery pig performance and metabolism. We hypothesized that enteric coronavirus infection would reduce pig performance, disrupt intestinal function and barrier integrity, and repartition energy and nutrients away from lean tissue accretion in post-weaned growing pigs. To address the overall objective, this dissertation has been organized into three research chapters.;The first study (Chapter 2) highlighted the negative impact of PEDV (US/Iowa/18984/2013) challenge on growth performance from day post inoculation (dpi) 0--7, while demonstrating that PDCoV (US/Iowa/25573/2014) challenge did not negatively impact growth performance of nursery pigs. The initial impact of PEDV challenge on growth performance within dpi 0--7, resulted in reduced protein accretion over 42 days. As a result of the lack of disease and performance impact in nursery pigs due to PDCoV challenge, Chapters 3 and 4 focused on further characterizing the effects of PEDV challenge in growing pigs. In Chapter 3, PEDV pigs were euthanized at dpi 2, 5, 7, and 14 to longitudinally assess intestinal function and integrity in nursery pigs during peak PEDV infection and during recovery. PEDV challenge resulted in compromised barrier integrity and digestive and absorptive function during peak infection, but returned to levels of Controls by dpi 7. Interestingly, PEDV challenge resulted in increased acidic mucins, specifically sialomucins, after PEDV was no longer present in jejunum compared with Controls. Chapter 4 PEDV challenged pigs had an overall (dpi 0--20) reduction in feed efficiency driven by the increased ADFI from dpi 6--20 compared with Controls. Further, these PEDV pigs had reduced efficiency of protein translation in jejunum at dpi 5 which was driven by reduced total protein; however, cell proliferation was greater at dpi 5 compared with Controls suggesting PEDV pigs were working to recover absorptive capacity and damage due to infection. Increased feed intake in PEDV pigs appeared to be providing enough energy and nutrients required by the epithelial layer to recover as PEDV pigs did not increase markers of muscle proteolysis (except for 20S proteasome) or increase liver or jejunum gluconeogenesis. Overall, the work from this dissertation showed that PEDV challenge directly influences intestinal function and integrity and modulates growth performance leading to long-term impacts on protein accretion in post-weaned growing pigs. Interestingly, PDCoV challenge did not negatively impact performance or tissue accretion in post-weaned growing pigs. The reduction in feed efficiency of PEDV pigs may be due to the allocation of feed energy and nutrients to the epithelium to support the activated immune system and intestinal epithelium recovery, and thus, away from lean growth. Although less severe than in newborn-suckling pigs, PEDV challenge does result in reduced intestinal function and integrity, but this resolves within 14 days. However, this short-term impact results in reduced lean accretion and increased days to achieve final market body weight.