Complex sentence: Aside from importing bloodstock into the US, Hoomes also maintained his own racing stable and sizeable stud service in which his good friend, another influential horseman of the time, John Tayloe III, was a partner.
Split into simpler sentences: Aside from importing bloodstock into the US, Hoomes also maintained his own racing stable and sizeable stud service. It seems that a good friend, another influential horseman of the time, John Tayloe III, was a partner.