Impacts of dietary starch on exercise-induced inflammatory markers in yearling Quarter Horses

Abstract

In humans, intestinal microbiota are recognized to play key regulatory roles in inflammation. In horses, addition of dietary starch is known to alter the intestinal microbiome, but the relationship between diet and inflammation in horses is poorly understood. To test the hypothesis that a starch-based diet would result in greater inflammatory markers than a fiber-based diet, Quarter Horses (mean ± SD 14 ± 1 mo; 337 ± 30 kg) were acclimated to a basal diet of 1% BW per day of a high fiber concentrate (36.3% NDF, 8.5% starch) and 1.5% BW per day coastal Bermudagrass hay in individual runs. Following 21 d of acclimation, horses were stratified by age, sex, and BW and randomly assigned to receive either the basal diet (CON; 7 fillies, 8 geldings) or hay plus 1% BW per day of an isocaloric, isonitrogenous starch concentrate (STARCH; 24.1% NDF, 28.7% starch; 8 fillies, 7 geldings) for 24 d. Concentrations of serum amyloid A (SAA), C-reactive protein (CRP), and plasma tumor necrosis factor (TNF)α, interleukin (IL)4, IL8, and IL10 were quantified from blood collected on d 0, d 21, and before (pre), and 0, 1, 6, 24, and 48 h after a 2-h submaximal exercise test (SET) on d 22. Data were analyzed using PROC MIXED in SAS v9.4 with a repeated effect of time and horse (diet) as a random effect; sex, time, diet, and time × diet were fixed effects. Regardless of diet, CRP increased and IL4, IL10, and TNFα decreased from d 0 to 21 (P ≤ 0.02). In response to the SET on d 22, CRP increased at 24 h in all horses (P < 0.0001). In STARCH horses, CRP then decreased to 48 h (P = 0.002), returning to pre values. In CON horses, CRP decreased to 48 h (P = 0.05) but remained above pre (P = 0.0005), resulting in CON having greater CRP than STARCH horses at 48 h (P = 0.02). In STARCH horses, TNFα increased from pre to 1 h (P = 0.02), then returned to pre levels by 6 h. In CON horses, TNFα increased above pre at 24 h (P = 0.04) and remained elevated at 48 h (P = 0.0005), resulting in STARCH tending to have greater TNFα than CON horses at 48 h (P = 0.06). Throughout the SET, CON horses had greater IL10 than STARCH (P = 0.005) but SAA, IL4, and IL8 were not affected by diet. In all horses, SAA increased at 6 h, continued increasing to 24 h, then decreased to 48 h but did not return to pre (P ≤ 0.007). IL8 increased at 1 h, continued to increase to 6h, and remained elevated through 48 h (P ≤ 0.02). Following the SET, IL4 remained stable until decreasing at 48 h to below pre (P < 0.0001). IL10 increased from pre to 0 h, then decreased at 24 h and was below pre at 48 h (P ≤ 0.03). Contrary to our hypothesis, these data suggest horses on a higher fiber diet may elicit a more robust acute inflammatory response in response to exercise.