PUBERTAL DEVELOPMENT OF RAM LAMBS: REPRODUCTIVE HORMONE CONCENTRATIONS AS INDICES OF POSTPUBERTAL REPRODUCTIVE FUNCTION

Abstract

Pubertal changes in blood serum concentrations of LH, FSH, PRL and testosterone were determined for 14 Suffolk rams born in March, and related to their postpubertal reproductive function. Blood samples were taken from the jugular vein (20-min intervals for 6 h) every 20 d and scrotal circumference and testicular diameter (TD) were measured every 10 d between the ages of 30 and 190 d, and at 13 and 17 mo. Daily sperm output (DSO, sperm voided in urine) or semen quality, and libido were assessed at about 6, 13 and 17 mo of age. LH-pulse magnitude increased between 30 and 70 d of age and then declined progressively to adult values; pulses occurred most frequently at 110 and 190 d of age, and at 17 mo. Mean concentrations of FSH, PRL and testosterone were highest at 50, 90 and 190 d of age, respectively, and changed normally with season when the rams were yearlings. Mean testosterone concentration at 50 d was related (P < 0.05) to testicular size (r ≥ 0.57) at all postpubertal ages and to ejaculation frequency (EF) (r = 0.82) at 6 mo and DSO (r = 0.78) at 13 mo. Mean and baseline concentrations of LH at 50 d were related (r ≥ 0.55, P < 0.05) to TD and DSO at 6 and 13 mo of age, and to EF at 6 mo. The strongest relationships (r ≥ 0.67, P < 0.01) were between mean testosterone concentration at 150 d and testicular size and sperm output at all postpubertal ages. Testicular size and spermatogenic function in yearling Suffolk rams relate to serum LH and(or) testosterone concentrations in the neonatal period (50 d) and at puberty (150 d). Key words: Sexual maturation, reproductive traits, interrelationships, ram