gs

ol N 5 nor al s an testicular growth that occurs after 25 weeks of age, when serum gonadotropin concentrations are low. Separate groups of Hereford!Charolais calves (nZ6) were castrated every 4 weeks from 5 to 33 weeks of age and at 56 weeks of age. A week prior motility (Wolf et al. 1965). Age at puberty varies with breed: in Hereford bulls it occurs between 39 and 52 from 4 to 32 weeks of age (Amann & Walker 1983). cells: fetal and adult Leydig cells, which differentiate from mesenchymal cells prenatally and postnatally respect-to the period of 16–28 weeks of age (McCarthyet al.1979, During the early rise in serum LH concentrations, serumDOI: 10.1530/rep.1.00768testosterone concentrations are low, increasing markedly q 2006 Society for Reproduction and FertilityCurtis & Amann 1981, Amann 1983). Subsequen