Submitted to: Journal of Animal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/3/2005
Publication Date: 9/1/2005
Citation: Jimenez-Severiano, H., Mussard, M.L., Fitzpatrick, L.A., D'Occhio, M.J., Ford, J.J., Lunstra, D.D., Kinder, J.E. 2005. Testicular development of Zebu bulls after chronic treatment with a gonadotropin-releasing hormone agonist. Journal of Animal Science. 2005. v. 83(9):2111-2122. Interpretive Summary: The use of herd sire registries and artificial insemination in the cattle industry have placed greater importance on larger testicular size and increased sperm production in stud bulls. Pituitary hormones play an important role in both pubertal development and mature testicular function because they contribute to an environment that promotes the production of germ cells and assists their development into viable sperm in the testis. Increased basal levels of the pituitary hormones in bulls during development results in larger testes and increased sperm production. The present study evaluated the effects of treatment (i.e., for 3-12 mo duration between birth and 15 mo of age) with implants of a gonadotropin-releasing-hormone agonist, deslorelin, on testicular development in 54 young zebu-crossbred beef bulls in Australia. Testis mass and structure were examined upon castration of bulls at 19 mo of age. In addition, the effectiveness of a stain for the transcription factor GATA-4, a specific marker for Sertoli cell nuclei, was evaluated and total number of Sertoli cells per testis was determined. Based on the results of this study, treatment of Zebu bulls with deslorelin had no apparent beneficial effect on testis development, and deslorelin treatments initiated at 3 mo of age resulted in delayed puberty, significantly smaller testis and reduced sperm production without affecting Sertoli cell numbers at castration, compared to control bulls, regardless of treatment duration. For the first time in the bovine, staining for GATA-4 was shown to be a useful method for identifying and quantifying Sertoli cell nuclei in both pre- and post-pubertal bulls. These results provide new methods and insights that expand our understanding of factors that program and control testis function. Effective manipulation of these factors may ultimately allow producers to enhance mature testis size, sperm production and reproductive efficiency in bulls used as sires in the cattle industry.
Technical Abstract: The objective was to compare testis characteristics of Zebu bulls treated with the GnRH agonist deslorelin, at different times and for different durations during their development. An additional objective was to determine the usefulness of a stain for the transcription factor GATA-4 as a specific marker for Sertoli cell nuclei. Bulls (54) were allocated to nine groups (n = 6), and received s.c. deslorelin implants, as follows: G1, from birth to 3 mo of age; G2, from 3 to 6 mo; G3, from 6 to 9 mo; G4, from 9 to 12 mo; G5, from birth to 15 mo; G6, from 3 to 15 mo; G7, from 6 to 15 mo; G8, from 12 to 15 mo; and G9, control (no implant). Bulls were castrated at 19 mo of age. Paraffin sections (10 'm) were subjected to quantitative morphometry and GATA-4 immunohistochemistry. At castration, all G9 bulls (6/6) had attained puberty, while a smaller proportion (P < 0.05) had reached puberty in G2 (2/5) and G6 (1/6). Bulls in G2 and G6 also had smaller (P < 0.05) testis weight, compared with G9. Total volume of seminiferous epithelium, and total daily sperm production in G2 and G6 were only half of that observed in G9. Spermatids were observed in less than 50% of seminiferous tubules in G2, G6 and G7, compared with 82% in G9 (P < 0.05). Staining for GATA-4 was specific for and abundantly expressed in the Sertoli cell nucleus in both pre- and post-pubertal bulls, and no other cell nucleus inside the seminiferous tubule was positive for GATA-4. Total number of Sertoli cells was not affected by treatment (P > 0.05), but nuclear volume was smaller in G2 and G6 (P < 0.05), compared to controls. In conclusion, treatment of Zebu bulls with deslorelin had no apparent beneficial effect on testis development and delayed puberty when treatment was initiated at 3 mo of age. Staining for GATA-4 is a useful method for identifying and quantifying Sertoli cell nuclei in both pre- and post-pubertal bulls.