- Expertise article | May
- J. Alex Pasternak et al.
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) exposed to a natural polymicrobial disease challenge with an array of bacterial and viral pathogens. Levels of total thyroxin (T4) and triiodothyronine (T3) assessed in sera by radioimmunoassay (RIA), decreased significantly 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 association with viral load or strain. The results of this study demonstrate porcine susceptibility to thyroid disruption in response to disease challenge and demonstrate a relationship between this response and growth performance.