The effects of acute exercise on oxidative stress in the skeletal muscle and blood of yearling and mature horses

s / Journal of Equine Veterinary Science 33 (2013) 321-399 324 molasses to encourage consumption. Analysis of urine for ergot alkaloids confirmed levels high enough to elicit toxicosis. Horses were exercised 5 d/wk and subjected to four SET (1/horse/wk), in the third and fourth wk of each period. Each SET consisted of a 10 min warm up in an indoor arena followed byan outdoor trail ride covering 4,875m at the jog (2.1 m/s) and extended trot (3.9 m/s) that required 30-31 min to complete. Variables measured before, during and after the SET included rectal temperature (RT), heart rate (HR), respiration rate (RR), packed cell volume (PCV), blood lactate (BL), percent weight carried (%C), sweat production (SP) and skin temperature (ST) at the poll (STP), exterior forearm (STF) and inner gaskin (STG). One and five min post exercise measurements were taken outdoors with remainingmeasurements recorded indoors at 10, 20, 30, 60, 90,120 min. A composite of ambient air temperature, humidity and solar radiation (WBGT), was recorded during the SET and recovery. A horse effect (p<.05) was observed for HR during the SETand recovery, and for RR and RTexcept near the end of recovery.Regression analysis showed no effect of speed at the jog or extended trot on HR during the SET. Therewas no effect of %C on HR during the SET, however %C had an effect on RR at 90 min and STP at 60 min post SET (p<.02). Horses on TRT had lower HR (p<.05) at 8 of 12 observation points during the SET. Treatment did not affect SP during the SETor HR at 1, 5 and 10 min post exercise. Ergot alkaloids consumption did not affect RR at any time point. Values for RT and ST at 90 min of recovery did not differ from resting values. During the SET, WBGT had no effect on HR, however it did effect resting RT (p<.01) and RR at 10, 30 and 60 min post SET (p<.02). Results of the current study indicate that ergot alkaloids may affect the horse’s ability to perform during outdoor exercise and recover during hot humid