Circulating white blood cell counts after 6 weeks of E2 supplementation (vs. age-matched controls) were determined using a Hemavet 950DS (Drew Scientific, Miami Lakes, FL). E2 levels in serum collected 2 or 6 weeks post pellet placement, and stored at −80°C prior to assay, were assayed by the University of Virginia Center for Research in Reproduction Ligand Assay and Analysis Core using a commercially available mouse/rat estradiol ELISA (Calbiotech, El Cajon, CA)[38 (link)]. Markers of bone formation (rat/mouse P1NP) or resorption (mouse TRAcP 5b) were assayed in fasting serum collected 2 weeks after start of E2 supplementation (vs. age-matched controls) using commercially available ELISAs (Immunodiagnostic Systems, United Kingdom) [22 (link),25 (link)].