188. Gastrointestinal Tract (GIT) Barrier Function in Stressed Feedlot Cattle Fed Essential Oils.

Abstract This study evaluated the effects of essential oil (EO) blends on physiological responses of feedlot cattle before transport (d 57), immediately after transport (d 65), and following a 4-week recovery period (d 92). Thirtytwo cross-bred heifers (265 ± 25.9 kg) were blocked by body weight and assigned to one of four treatments (three EO blends or a control) on d 0. The basal diet was a 23% triticale hay and 22% corn silage based (DM basis) grower diet. Treatments were top-dressed daily at 300 mg/heifer. Heifers were exposed to naturally occurring heat stress (THI ≥ 68) and transported for 8 h on day 65. Blood gases, pulse oximetry, inflammatory markers, and urinary chromium (Cr-EDTA) excretion were assessed across three sampling periods (days 57, 66, and 92). Performance outcomes did not differ among treatments prior to transport (P ≥ 0.46); however, average daily gain from day 66 to 92 was greater for CON and EO blend 3 compared with EO blend 1 (P = 0.08). Transport induced shifts in respiratory acid–base balance, with EO blend 1 and 3 exhibiting greater partial pressure of carbon dioxide (P = 0.06) when compared to CON. EO blend 1 also exhibited elevated base excess in extracellular fluid (P = 0.10), an increase in bicarbonate (P = 0.07), as well as an increase in total carbon dioxide (P = 0.10) when compared to CON and EO blend 2, suggesting reduced post-stress ventilation and CO₂ clearance. EO blend 1 increased pre-transport perfusion index (Pi) (P = 0.05) compared to all other treatments and reduced pre-transport peripheral oxygen saturation (SpO₂) (P = 0.05) compared to CON and EO blend 2, whereas EO blend 3 demonstrated lower Pi (P = 0.03) compared to all other treatments during recovery. EO blend 1 and 3 showed greater SpO₂ during recovery (P = 0.02) when compared to CON and EO blend 2, indicating improved systemic oxygenation. Haptoglobin tended to be lower in EO blends 1 and 3 after transport (d 65) vs. CON (P = 0.06). Other inflammatory markers (LBP, IL-6, SAA) were not affected by treatment after transport (P ≥ 0.56). During recovery, EO blend 3 tended to have lower LBP (P = 0.07), and EO blend 2 had lower SAA (P = 0.09) compared to CON. Gut permeability, assessed via urinary Cr-EDTA excretion, did not differ overall among treatments at any timepoint (P ≥ 0.54). In conclusion these findings indicate that EO blends caused physiological responses to stress, with EO blend 1 modulating ventilatory and acid–base responses immediately after transport and EO blend 3 supporting post-transport recovery, reflected by improved oxygenation and reduced inflammatory markers. Essential oils may offer a targeted nutritional strategy to increase resilience to stress in growing cattle, though treatment-specific mechanisms still require further investigation.