A Longitudinal Study of Pubertal Development in Boars Investigation of the Relationships Between Gonadal and Epididymal Development and Plasma Luteinizing Hormone and Testosterone Profiles

A longitudinal study was undertaken to evaluate the course of gonadal and epididymal development, and the concurrent endocrine changes during the period of sexual maturation, in Large White x Landrace boars.
Twenty-four animals were castrated sequentially at ages ranging from 43 to 241 days. Increases in testicular weights were more highly correlated with body weight (r = 0.953, P <0.001) and age (r = 0.919, P <0.001) than were similar increases in epilidymal weights (r = 0.558 and 0.593, P < 0.01, respectively). The age at onset of spermatogenesis varied between boars in the range 90 to 127 days. First observations of spermatozoa in seminiferous and epididymal tubules were made at 127 and 146 days of age respectively. Epididymal spermatozoal reserves per epididymis (ESR) were zero prior to 146 days of age; from that age mean ESR values increased progressively from 5.54 times 10⁹ to 130 times 10⁹ at 241 days of age.
Longitudinal profiles of luteinizing hormone (LH) and testosterone secretion were investigated by assaying plasma samples collected at fortnightly intervals from each of ten boars aged 42 to 236 days. Until 82 days of age mean LH levels were low (0.20–1.25 ng/ml), then rose to a peak of 2.19 ng/ml at 110 days. Later LH levels declined gradually and after 166 days fluctuated between 0.5 and 1.0 ng/ml. Mean testosterone levels also were low in the prepubertal period (0.10–0.27 ng/ml), then between 110 and 138 days increased from 0.60 to 8.00 ng/ml. Subsequently testosterone concentrations fell slowly, then except for an isolated peak of 7.73 ng/ml at 194 days, fluctuated between 1.40 and 3.80 ng/ml. Castration ***