Effects of exogenous equine somatotropin on mineral balance in two-year-old horses in race training

This study examined the effects of exogenous equinesomatotropin (eST — Equigen) administration on mineral absorption and retention in two-year-old horses in race training. Sixteen Quarter Horse geldings were paired by age (ave.age=794 d), and one horse from each pair was assigned at random to either the eST treatment group or the control. The experiment was conducted over 112 days during which the horses were gentled to ride and trained on a dirt track in a regimen typical for race horses in training. At 28-day intervals, collections of total fecal and urinary output were made to determine effects on Ca, inorganic P, Mg, Cu and Zn mineral balance. Due to marginal and slightly deficient amounts (P<01)of Ca, P, Mg and Zn intake by days 84 and 112, a result of reduced feed intake to maintain a constant body condition in the presence of a decreased workload, mineral balance for the aforementioned minerals was only examined through day 56. In contrast to the previous minerals, Cu intake appeared adequate. Ca, P, Mg, Cu and Zn intake did not differ (P>.05) by treatment. The eST-treated horses increased (P<.05) Ca retention as a percent of Ca absorbed, had greater (P<.05) overall apparent efficiency of P absorption and greater (P<.05) apparent retention of P on day 56 than the control horses. The eST-treated horses had greater (P<.05) apparent Cu absorption on day 56, greater (P<.05) apparent Cu absorption efficiency on days 56 and 84, and there was a trend (P<.1) for the eST-treated horses to retain more Cu on day 56 than the control horses. Finally, the eST-treated horses retained a greater percent (P<.1) of absorbed Zn on day 56.