Testicular development, histology, and hormone profiles in three yearling angus bulls with spermatogenic arrest

Abstract

This article discusses the interactions between testis criteria and hormone profiles in Angus bulls with spermatogenic arrest. From 2 to 12 months (mo), testis diameter and hormone concentrations (basal and GnRH-stimulated) were evaluated in 27 bulls. At 12 mo, testes were excised. The z statistical test was used to determine whether parameters in three infertile bulls were different (P < 0.05) from those in 24 bulls with normal spermatogenesis. Bull 1 had Sertoli cell-only syndrome and Bull 2 had 90% of the tubules without germ cells and only A1 spermatogonia in the remaining. In Bull 3, germ cells did not advance beyond the primary spermatocyte stage. At 12 mo, testes of Bull 1 (99 g), Bull 2 (105 g) and Bull 3 (32 g) weighed less than those of normal bulls (251.5 ± 56 g). Sertoli cell numbers/testis in Bull 1 (3.8 × 10 9) and Bull 2 (4.3 × 10 9) were not different from those in normal bulls (4.9 ± 0.3 × 10 9), but were reduced in Bull 3 (1.6 × 10 9). The number of Leydig cells per gram of testis parenchyma was higher in Bull 1 (5.4 × 10 7), Bull 2 (7.3 × 10 7) and Bull 3 (19 × 10 7) than in normal bulls (3.6 ± 0.2 × 10 7). In Bulls 1 and 2, basal and GnRH-stimulated LH, FSH, testosterone (T), androstenedione (Δ 4A) and estradiol 17-β (E 2) were within normal ranges at most ages. However, basal FSH and LH were greater in Bull 3 than in normal bulls, probably the causes for higher Leydig cell density. Also in the same animal, GnRH induced lower responses in LH and FSH, consequence of low basal T and E 2 at some ages. Basal and GnRH-stimulated Δ 4A in Bull 3 were greater than in normal bulls after 6 mo, indicating impairment of Leydig cell differentiation. Deficiency in hormone secretion did not appear to be the cause of infertility, which points toward impaired gonadal responses or secretion of intratesticular factors, or genetic defects. Moreover, infertile animals may not always show pronounced changes in hormone secretion, but evaluation of testis growth around puberty can help identify those animals that do not proper gonadal development.