PUBERTAL DEVELOPMENT OF RAM LAMBS: BODY WEIGHT AND TESTICULAR SIZE MEASUREMENTS AS INDICES OF POSTPUBERTAL REPRODUCTIVE FUNCTION

Abstract

The relationship between the pattern of early testicular growth and postpubertal spermatogenic function and libido was investigated with 14 Suffolk rams born in March. Scrotal circumference and testicular diameter (TD) measurements were taken every 10 d between 30 and 190 d of age, and at 13 and 17 mo. Daily sperm output (DSO, sperm voided in urine) or semen quality, and libido were assessed at approximately 6, 13 and 17 mo of age. At 6 mo of age, rams with the larger testes had a greater DSO (r ≥ 0.77, P < 0.01) and mated estrual ewes more frequently (r ≥ 0.72, P < 0.01). Rams with larger testes at 13 mo had a greater DSO (r ≥ 0.74, P < 0.01), and those with larger testes at 17 mo ejaculated a higher percentage of motile spermatozoa (r ≥ 0.55, P < 0.05) and a greater number of spermatozoa (r = 0.61, P < 0.05; TD only). DSO at 13 mo was related to testicular size (r ≥ 0.54, P < 0.05) between 150 and 190 d of age. There were also correlations between the number of spermatozoa ejaculated at 17 mo and testicular size measurements (r ≥ 0.56, P < 0.05) taken between 170 and 190 d. However, ejaculation frequency (EF) at both 13 and 17 mo was not related to earlier testicular size measurements. Whereas testicular size and spermatogenic function of yearling Suffolk rams relate to testicular size measurements taken at about 6 mo of age, juvenile testicular size measurements correlate with EF only in the immediate postpubertal period. Key words: Sexual maturation, reproductive traits, interrelationships, ram