Effects of Exercise on Bone Metabolism in Yearling Horses

Abstract

Sixteen yearling Quarter Horses were used in a split-plot-designed experiment to determine the effects of exercise on bone metabolism. Horses were blocked by sex and BW and then randomly assigned to either the exercised (EX) or non-exercised (NEX) treatment. Diets were formulated to meet or exceed NRC requirements for yearlings in moderate growth. Diets were fed at 2.5% of BW and consisted of a pelleted concentrate, prairie grass hay, and alfalfa cubes in a 50:30:20 ratio, respectively. Radiographs of the third metacarpal (MCIII) were taken on d 0, 45, and 90 for determination of radiographic bone aluminum equivalence (RBAE). Blood was taken every 14 d throughout the trial to measure carboxy-terminal propeptide of type I procollagen (PICP) and carboxy-terminal telopeptide of type I collagen (ICTP) concentrations in serum. Although no differences between treatments were found in RBAE within days measured, a significant decrease in RBAE was observed between d 0 and 90 for the NEX horses. This decrease in bone optical density throughout the duration of the trial indicates that stalling and lack of exercise may result in a greater loss of bone mineral content (BMC) as compared with horses that were forced to exercise. Consequently, the EX horses may be better prepared for future mechanical stresses placed upon them.