Effects of a forage-only diet on body weight and response to interval training on a track

The effect of a forage-only diet on body weight (BW) and response to interval training was studied in standardbred horses in training. Six geldings were fed a forage-only diet (F, early cut) and a forage/concentrate diet (C) including haylage (late cut, same crop) and concentrate (82 % oats) in a change-over design for 29 days. The feed allowances were isocaloric and iso-nitrogenous. On day 17 an interval training test was performed on a track (6 km warm-up, 4 intervals of 600 m at a predetermined velocity of 10.5-13 m/s, approx. 0.6 % incline). BW was measured before, 15 min and 24 hours after the test. Heart rate was measured before and until 120 min post exercise and breathing frequency until 60 min post exercise. The exercise temperament was assessed by the drivers using a linear index. A blood sample was taken immediately after the last interval for analysis of plasma lactate (pLa). The pre-exercise BW tended to be higher and the 24 h post exercise BW was higher on diet F compared to diet C. There was no significant difference in pLa and temperament index although some individuals showed a numerical increase on diet C. Heart rate and breathing frequency was higher on diet C. In conclusion, a high energy forageonly diet might increase BW but this does not seem to have any impact on performance related parameters during field conditions. In contrast, diet C might have affected the psychological response to exercise and thereby some physiological parameters.