PS11-25. Effects of Dietary Additives on Antioxidant Activity After Submaximal Exercise in Juvenile Horses.

Abstract Juvenile horses undergo intensive exercise programs that increase oxidative damage and decrease antioxidant activity, which can impair recovery. Dietary additives may help sustain systemic antioxidant activity during strenuous activity. This study aimed to evaluate the effect of a dietary additive that provides gastric buffering, pre-, pro-, and post-biotics, and trace mineral fortification on circulating antioxidant activity following a submaximal exercise test (SET). It was hypothesized that the dietary additive would maintain or increase antioxidant activity. To test this, twenty 2-year-old stock-type horses, balanced by body weight (BW; 417 ± 35 kg) and sex, were given 0.75% BW concentrate daily, either without dietary additives (CON; n = 10) or with a blend of pre-, pro-, and post-biotics, marine calcite, and organic trace minerals (Digestive Shield; DS; n = 10). On d 0, horses started supplementation and a progressive exercise regimen, increasing in intensity every 7 d, with a 1-h SET performed on d 30. Blood samples were collected via jugular venipuncture on d 0, before (PRE), immediately after (POST), 0.5, and 1 h after the SET to measure circulating catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx) activities. Data were analyzed using PROC MIXED in SAS with fixed effects for dietary additive, time relative to SET, and their interaction. The effect of sex was not significant (P > 0.05) and was removed to conserve degrees of freedom. Significance was set at P ≤ 0.05, and trends were 0.05 < P ≤ 0.10. Circulating CAT activity was greater in DS horses (108.9 ± 11.9 nmol/min/mL) than in CON horses (53.3 ± 13.3 nmol/min/mL; P < 0.01). The dietary additive did not impact GPx (CON: 368.5 ± 18.5; DS: 372 ± 16.3 nmol/min/mL; P = 0.80) or SOD activity (CON: 4.3 ± 0.3; DS: 3.9 ± 0.4 U/mL; P = 0.50). Catalase activity was lowest at d 0 (d 0: 43.8 ± 20 nmol/min/mL) compared with all timepoints (PRE: 66.4 ± 20.0; POST: 86.2 ± 20.0; 0.5 hr: 88.8 ± 20; 1 hr: 120.1 ± 20.0 nmol/min/mL;P ≤ 0.10). Superoxide dismutase activity was greatest 1 h post-SET (6.0 ± 0.60 U/mL; P < 0.01) compared with all other timepoints (d 0: 2.9 ± 0.60; PRE: 3.9 ± 0.60; POST: 4.0 ± 0.60; 0.5 h: 3.7 ± 0.60 U/mL). Circulating GPx activity was lowest at d 0 (d 0: 254.9 ± 26.1 nmol/min/mL; P < 0.01) compared with all timepoints (PRE: 381.3 ± 26.1; POST: 409.02 ± 26.7; 0.5 hr: 393.7 ± 29.7; 1 hr: 412.5 ± 26.7 nmol/min/mL). The dietary additive with gastric buffering, pre-, pro-, and post-biotics, and trace-mineral fortification increased circulating CAT activity but not SOD or GPx activity, and did not affect activity following the SET in juvenile horses.