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Summary Thirty mixed‐bred foals aged 2.5–6.5 months (mean 4.6 ± 1.0 months) with no clinical or radiographic signs of dyschondroplasia (DCP) were fed one of four diets for 16–18 weeks. Twelve foals were fed a Control diet which comprised ˜100% of the NRC recommendations for dietary energy (DE) and crude protein (CP). Six were fed a diet with ˜126% of NRC levels for CP and 12 foals were fed a diet with 129% of NRC levels for DE. The diets comprised 3 different formulations of rice‐based pellets with added maize oil for the High DE diet, and oaten chaff. Average daily gain, humeral length and wither height were slighly, but not significantly, different in the foals on the High DE diet than in those fed the Control or High CP diet. Clinical and radiographic signs of DCP were seen in 6 out of 12 foals fed the High DE diet. Not one of the foals fed High CP or Control diets showed any clinical and radiographical signs of DCP. The number and severity of DCP lesions found at post‐mortem examination were much greater in the High DE foals than in the Control and High CP foals. Multiple lesions of DCP were detected in 11 foals fed the High DE diet, in 1 foal fed the High CP diet and in 1 foal fed the Control diet. Histological lesions of DCP were confirmed in 18 foals; in all 12 of the High DE foals, 4 of the 6 High CP foals and 2 of the 12 Control foals. The number of histological lesions of DCP were significantly greater in the High DE foals than in the Control group (P < 0.0001). The incidence of lesions of DCP in the foals fed High CP was not significantly different from that in the Control foals (P = 0.11).

Stacked rectangular rosette strain gages were used to measure surface bone strain on the dorsomedial cortex of the third metacarpal bones in 6 adult Thoroughbred horses during treadmill exercise. The peak principal compressive and tensile strains, angle of the peak strains and strain rate during loading were calculated and compared with speed and gait. At speeds from 4 to 14 m/s loading on the metacarpus resulted in compression of the dorsomedial cortex. Tension only occurred consistently in 1 forelimb of 1 horse at the walk (2 m/s). The angle of peak compression was within 10° of the longitudinal axis of the bone, and the magnitude of compression was proportional to the speed of exercise. Mean maximum compressive strains in the 6 horses at 2 m/s were –668 µstrain, –1,204 µstrain at 4 m/s; –1,617 µstrain at 6 m/s; –2,127 µstrain at 8 m/s, and –2,533 µstrain at 10 m/s. Recordings from 3 horses gave a mean –3,206 µstrain at 12 m/s, and strains at 14 m/s approached –4,000 µstrain. Peak strains were similar in both forelimbs at the canter while strain rate tended to be higher in the leading forelimb.

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