PSVI-14 Mitigating the Negative Effects of Heat Stress in Grow-Finish Pigs Using Water Delivered Oregano Essential Oil
Authors: Turner Isabel , Young Candace , Brizgys Lauren A , Scaff Taw , Richert Jacob A , Richert Brian T , Pasternak Jonathan A , Radcliffe John Scott 
Published: October 2023

Abstract
Grow-finish pigs (n = 192) were used in a 28-day experiment to determine if adding oregano essential oil to the water would mitigate the detrimental effects of heat stress. Pigs (initial BW = 51.9 kg) were blocked by sex and BW and randomly allotted to a 2x2 factorial arrangement of water treatment (oregano essential oil vs. control) and environment (heat stress vs. thermoneutral). There were 6 pigs/pen (4 barrows and 2 gilts/pen) and 8 pens/treatment. Pigs were given 15 d to acclimate to pens and water treatment under thermoneutral conditions (21.1℃). Following acclimation, one-half the pigs were subjected to a 3-day diurnal heat stress (12 h at 33.3℃ and 12 h at 26.7℃). On d 22 of the experiment (3 d post-heat stress), one barrow/pen was euthanized; jejunal mucosa scrapings were collected, flash frozen in liquid nitrogen, and stored at -80oC for subsequent RNA isolation and cDNA creation. Gene expression of CDKN1A, TP53, GPX1, SOD1, SLC2A2, SLC2A5, and MUC2 were determined by qPCR using SYBR green, normalized using housekeeper genes and expressed relative to the control treatment using the 2-ΔΔCT method. Data were analyzed as RCB using GLM procedure in SAS 9.4 with fixed effects of water treatment, environment, and the interaction. Heat-stressed pigs had reduced ADG (P &lt; 0.003) and Gain:Feed (P &lt; 0.008) during the 3d heat stress compared with pigs housed in thermoneutral conditions. Post-heat stress, ADG (P &lt; 0.001) and Gain:Feed (P &lt; 0.001) increased in previously heat-stressed pigs compared with thermoneutral pigs. There was no effect of oregano supplementation before or during heat stress. However, in the post-heat stress period, ADG was increased (P &lt; 0.05) by oregano supplementation in the water for both heat stressed and non-heat stressed pigs. Oregano supplementation did not affect ADFI before heat stress. An interaction (P &lt; 0.005) of heat stress and water treatment was observed for ADFI during heat stress and after heat stress. During heat stress, oregano supplementation resulted in reduced feed intake. Post-heat stress ADFI was lowest for non-heat stressed pigs with no oregano supplementation. Oregano essential oil increased water consumption before (P &lt; 0.02), during (P &lt; 0.03), and after heat stress (P &lt; 0.02), with an overall increase in water consumption of 35% compared with control pigs (P &lt; 0.04). No interactions of heat stress and oregano supplementation were observed for gene expression. SLC2A2 expression tended (P &lt; 0.08) to be downregulated when oregano essential oils were added to the water and upregulated following an acute heat stress. SLC2A5 expression was increased in pigs given oregano compared with control pigs (P &lt; 0.02), but was unaffected by heat stress. Water delivered oregano essential oil increased water intake and had a slight effect on intestinal gene expression but did not mitigate the effects of a short-term heat stress.