PSII-B-21 - Does Prior Viral Infection Exacerbate the Response to Heat Stress?

Abstract: In rodent models, prior immune activation appears to exacerbate the response to heat stress (HS), presumably by compounding an inflammatory response by both insults. Thus, study objectives were to investigate whether prior viral infection aggravates the physiological and feed intake (FI) responses to HS. Crossbred barrows (n=45; 75.5±4.8 kg BW) were enrolled in two experimental periods (P). During P1 (2 d), pigs were fed ad libitum and housed in thermoneutral (20ºC) conditions. During P2 (6 d), pigs were exposed to an increased heat load (28 to 31ºC). Rectal temperature (T_R), skin temperature (T_S), and respiration rate (RR) were obtained twice daily. FI was measured daily as feed disappearance. Unexpectedly, pigs became sick during the experiment and tested positive for influenza on d 6 of P2. Based on T_R obtained during P1, animals were retrospectively categorized into 1 of 2 groups: 1) High-T_R (HT; top third of pigs; T_R>39.32ºC; x̅=39.38ºC; n=15), or 2) Low-T_R (LT; bottom third of pigs; T_R < 39.10ºC; x̅=38.95ºC; n=15). Pigs in the middle third tier were excluded from the analysis. This ostensibly categorized pigs into a “sick” and “healthy” status. Data were statistically analyzed using the MIXED procedure in SAS. As expected, HS increased T_R in both groups; however, HT had elevated T_R during P2 relative to LT pigs (+0.5ºC; P < 0.01). Skin temperature and RR increased during HS but remained similar between HT and LT pigs (P>0.41). During P1, FI was similar between groups (P>0.33). During P2, HS reduced FI in both groups; however, the decrease was more severe in HT than LT pigs (53 vs. 37%, respectively; P=0.01). Altogether, HT pigs, presumably infected before HS exposure, had increased T_R and a more drastic reduction in FI during HS than LT pigs. A better understanding of how viral or bacterial infection influences the response to HS would have pragmatic implications for all segments of animal agriculture.