NEGATIVE RELATIONSHIPS BETWEEN BLOOD-CONCENTRATIONS OF FOLLICLE-STIMULATING-HORMONE AND TESTICULAR SIZE IN MATURE BOARS

Relationships between blood concentration of FSH and testicular size a nd daily sperm production were evaluated with data obtained from five studies originally designed to investigate regulation of FSH secretion in Meishan (MS), White composite (WC), and crossbreds of these. A min imum of three blood samples/boar were obtained at greater than 4-d int ervals for determination of FSH, and testes were obtained at castratio n or slaughter. In a random sample of boars, FSH was fivefold greater (P < .01) in MS than in WC boars (n = 22/group). Daily sperm productio n (DSP)/gram of testis (estimated by counting elongated spermatid nucl ei in testicular homogenates) was similar in the groups, but testicula r weight (TWT), adjusted for body weight, was less (P < .01) in MS tha n in WC, yielding lower total daily sperm production (TDSP; P < .05) i n MS boars. In four populations (one with MS, one with WC, and two wit h crossbreds; n = 34 males), boars were selected for extremes in FSH c oncentrations from larger groups. Across all populations, a threefold greater plasma FSH concentration was associated with a 32% smaller TWT (P < .01). Coincident with increased FSH, TDSP was 33% less (P < .05) . In 48 MS x WC boars that were selected for divergence in plasma FSH during pubertal development (4 to 6 mo of age), this divergence was re tained at 1 yr(P < .01). Retrospectively, the divergence in FSH was al so apparent at 2 and 8 wk of age (P < .05), and the boars with elevate d FSH had smaller testicles, lower DSP, and lower TDSP (P < .01). Thes e studies document a negative relationship in mature boars-between FSH secretion and testicular size accompanied with decreased TDSP.