Thyroid dysfunction in feeder pigs following polymicrobial or porcine reproductive and respiratory syndrome virus-2 challenge

Authors: PASTERNAK, ALEX - Purdue University; MACPHEE, DJ - University Of Saskatchewan; Lunney, Joan; ROWLAND, RRR - University Of Illinois; DYCK, MK - University Of Alberta; FORTIN, F - Quebec Pork Development Centre Inc; DEKKERS, JACK - Iowa State University; PLASTOW, GS - University Of Alberta; HARDING, JOHN CS - University Of Saskatchewan

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2021
Publication Date: 11/3/2021
Citation: Pasternak, A., Macphee, D., Lunney, J.K., Rowland, R., Dyck, M., Fortin, F., Dekkers, J., Plastow, G., Harding, J. 2021. Thyroid dysfunction in feeder pigs following polymicrobial or porcine reproductive and respiratory syndrome virus-2 challenge. Journal of Animal Science. 99:(911)1-13. https://doi.org/10.1093/jas/skab325.
DOI: https://doi.org/10.1093/jas/skab325

Interpretive Summary: Thyroid hormones are powerful regulators of growth and development; notably, they can be altered when animals are severely stressed or ill. This study tested the role of thyroid hormones, thyroxin (T4) and triiodothyronine (T3), in pig disease responses, testing serum samples from nursery-aged pigs after natural polymicrobial disease, or specific viral infection, challenges. Pigs from high health farms showed no change in either T3 or T4 when managed under standard industry conditions. Serum levels of T4 and T3 decreased significant by 7 to 14 days post challenge and were correlated with average daily weight gain. Post challenge T3 and T4 levels rebound with higher hormone levels associated with high average daily weight gain, with no difference associated with viral load. This data may provide insight into mechanisms by which the pig can starve a pathogen of resources required for replication.

Technical Abstract: Thyroid hormones are powerful regulators of growth, development and basal metabolic rate and can be dysregulated under conditions of severe stress or illness. To understand the role of these hormones in porcine disease response, serum samples were obtained from 3 batches of nursery-aged pigs (n=208) following natural polymicrobial disease challenge with an array of bacterial and viral pathogens. Levels of total thyroxin (T4) and triiodothyronine (T3) assessed in sera by RIA, decreased significant by 14 days post exposure (DPE). Levels of T3 partially rebounded by 48 DPE, while T4 levels remain depressed. Post-exposure T3 and T4 levels were positively correlated with acute and long-term average daily gain. Cross-sectional sampling of animals maintained at the high health source farms, showed no equivalent change in either hormone when managed under standard industry conditions. To further elucidate the effect of PRRSV-infection on thyroid hormone levels, archived sera over 42 days post inoculation (DPI) from nursery pigs (N=190) challenged with one of two PRRSV2 strains by the PRRS Host Genetics Consortium (PHGC) were similarly assessed, with animals selected in a two-by-two design, to investigate biological extremes in average daily gain (ADG) and viral load. All animals showed a similar decrease in both thyroid hormones reaching a minimum at 7 DPI and returning to near pre challenge levels by 42 DPI. Post challenge T3 and T4 levels were significantly greater in high ADG groups, with no significant difference association with viral load or strain.