PS5-8. The Effects of Transportation and Submaximal Exercise on Stress Responses in Mature Horses.

Abstract Performance horses are frequently transported to and from events requiring intense exercise, but the combined physiological effects of transportation and exercise have not been well characterized. Therefore, the objective was to evaluate the effects of transportation and submaximal exercise on stress markers in mature horses. Hypothesizing that the combined effect would increase stress mediators more than transport alone. Sixteen mature stock-type horses were housed individually and fed to meet nutritional requirements for horses in light exercise (5 d/wk). Horses were randomly assigned to 1 of 3 treatments: transport and exercise (T+E; n = 6), transport only (TT; n = 6), or a negative control (CON; n = 4). Both T+E and TT horses were transported for 1 h, then T+E horses completed a 1 h submaximal exercise test (SET) while TT horses were held in individual pens, after which T+E, and TT horses were transported again for 1 h. Throughout this, the CON horses remained stalled but samples were collected at the same intervals as T+E and TT. Blood samples were collected pre-transport I (Pre TR1), post-transport I (TR1), post-SET, post-transport II (TR2), and 2 h post TR2 to evaluate cortisol and interleukin (IL-) 4, 8, 10, and tumor necrosis factor-α (TNF-α). Data were analyzed using PROC MIXED in SAS, with significance set at P ≤ 0.05, and trends were 0.05 < P ≤ 0.10. Cortisol tended to be affected by treatment and time (P = 0.06). Cortisol Pre TR1 did not differ (P ≥ 0.50). After TR1, TT had 72% greater cortisol than CON (P < 0.01), but did not differ from T+E horses (P = 0.32). Cortisol POST SET was 68% greater in T+E horses than in CON (P = 0.04), and TT horses did not differ (P = 0.38). Following TR2, cortisol was 80% and 86% greater in TT and T+E horses, respectively, than in CON horses (P ≤ 0.04). Cortisol concentrations 2 h after TR2 did not differ (P ≥ 0.49). There was an overall effect of treatment for TNF-α which was 145% and 118% greater in CON and TT, respectively, than in T+E horses (P ≤ 0.01). Interleukin-8 was also influenced by treatment and was 29% greater in TT horses than in T+E (P < 0.01), and CON horses were intermediate (P ≥ 0.15). Interleukin-4 tended to differ with TT 36% greater than CON horses (P = 0.09), but T+E did not differ (P ≥ 0.14). Interleukin-10 did not differ across treatments (P ≥ 0.12). Tumor necrosis factor-α, IL-4, 8, and 10 were not affected by the time (P ≥ 0.49). These findings suggest transportation increased stress responses in mature horses, while submaximal exercise did not further exacerbate these responses but altered inflammatory markers.