Bone density in the juvenile racehorse treated with exogenous somatotropin (eST)

Thirty juvenile horses were paired by age within sex, and one horse from each pair was randomly assigned to either eST treatment or to a control group. The horses were “broke” to ride and trained in a regimen typical for young racehorses. Radiographs were taken on days 0, 32, 50, 64, 82, 96 and 128 of the study. Increase in total radiographic bone aluminum equivalence (RBAE) was significantly greater in eST treated horses than in the control group (P<.003). Increase in medial RBAE was also significantly greater due to eST treatment (P<.0001). Trends were apparent for increases due to eST treatment in dorsal RBAE (P=.07) and lateral RBAE (P=.07). Bone density was selectively increased in the dorsal, lateral and medial vs. the palmar cortex in the eST treated horses.