The effects of forced exercise prior to race training on two-year-old racehorses

Abstract

The effects of forced exercise prior to race training hics. were investigated in two-year-old horses. of two treatment groups-one which received forced exercise and the other which served as a non-exercised control group. Sixteen geldings of Quarter Horse-type breeding were assigned to one The project began when the horses reached 15 months of age. Phase 1 consisted of 14 weeks of training three days per week on a high speed treadmill. The exercise program consisted of a warm-up period followed by two, l-min sprints. The sprints began in the third week of the program and progressively increased in speed. Following phase 1, all were placed in race training. Horses were broke to ride, trained to gallop on the track, and were kept in training for four, 28-d periods. Radiographs were taken of the left third metacarpal to determine bone density. Serum was collected and assayed for concentrations of calcium, osteocalcin, the carboxyterminal telopeptide of type l collagen (ICTP) and the carboxyterminal propeptide of type 1 procollagen (PICP). Urine collections were performed for analysis of deoxypyridinoline crosslinks (DPD) and creatinine. There was no difference due to treatment in RBAE values of the laterals medial, dorsal or palmar cortex during phase 1. However, in data normalized from d 0 of phase 1, the exercised group had a greater gain in total bone volume (P<.05). Also, ratios of bone in different locations indicated that the exercised group may have been preferentially laying down more bone in the dorsal and medial cortices and less bone in the palmar cortex. Initiation of race training appeared to limit gains in bone density in the lateral, dorsal and palmar cortex beyond d 42-1% of phase II. When data were normalized from the onset of race training, ICTP and PICP concentrations were higher in the pre-exercised horses (P<.05 and P<.l respectively) indicating higher rates of bone turnover. Overall, concentrations of PICP and ICTP were lower during phase II when compared to values seen in phase 1. Bone turnover appeared to be decreased during race training as supported by both the biochemical markers and radiographic evidence.