No abstract

Abstract.It has been well demonstrated that the quantity and quality of the semen obtained from bulls improve with age. To understand the relationship between the semen characteristics and hormonal conditions in Holstein bulls, age-related changes in serum levels of inhibin, FSH, LH and testosterone were investigated. One hundred three Holstein bulls were divided into 11 age-groups as 2.5 (n=10), 6.5 (n=10), 12 (n=12), 24 (n=9), 36 (n=10), 48 (n=12), 60 (n=13), 72 (n=8), 84 (n=5), 96 (n=8) and 108 (n=6) months old. Serum levels of inhibin, FSH, LH and testosterone were measured by specific radioimmunoassays. Serum levels of inhibin were highest in bull calves before 12 months of age, and significantly decreased at 12 months old and remained low thereafter. In contrast to inhibin, serum levels of gonadotropins and testosterone were low in young bulls, and then increased with age. In summary, the concentrations of inhibin, gonadotropins and testosterone in serum changed with age in Holstein bulls. Key words: Bulls, Gonadotropins, Inhibin, Testosterone.(J. Reprod. Dev. 46: [245][246][247][248] 2000) environment, management practices, physiological status and genetics. In general, semen from Holstein bulls for use in AI is collected from bulls that are 1 to 7 years old. The age of the bulls at the time of semen collection affects the volume of the ejaculate, the concentration of sperm and sperm motility. It has been well shown that all of these ejaculate characteristics increase as bulls age [1]. Spermatogenesis is regulated by several hormones of the hypothalamus-hypophyseal-gonadal axis. The hormones that are required to support spermatogenesis are FSH and testosterone [2]. Inhibin and LH are indirectly involved in -Originalrtificial insemination (AI) is the main tool used for genetic improvement of dairy cattle. The conception rate with AI depends on the characteristics of the semen that are cryopreserved in straws. To make a large number of straws, AI organizations try to collect the maximum amount of spermatozoa of the highest possible quality. The quantity and quality of semen (i.e. volume of ejaculate, concentration of spermatozoa in the ejaculate, and percentage of spermatozoa that are motile) produced by bulls are affected by the

This study investigates the differential localization of the alpha-subunit (S100-alpha) and the beta-subunit (S100-beta) of the S-100 protein in the feline testis, using immunohistochemistry with polyclonal antibodies to bovine S-100 protein (S-100) and monoclonal antibodies to bovine S100-alpha and S100-beta. Appreciable differences were observed in the cellular localization of the immunoreactivity of each subunit. S-100 was observed in the Sertoli cells, the epithelial cells of the transitional segment of the seminiferous tubules, Leydig cells and the peritubular cells of the seminiferous tubules, but was not observed in the epithelial cells of straight tubules and the rete testis or in the endothelial cells of blood and lymph vessels. S100-alpha immunoreactivity was localized in Sertoli cells, peritubular cells and the epithelial cells of the terminal segment of the tubules, whereas S100-beta immunoreactivity was localized in Leydig cells. The differential localization of the alpha- and beta-subunits of the S-100 protein in the feline testis suggests that this protein is multifunctional and be useful as an investigative tool in studying feline testis function.

Age-related changes in immunoreactive inhibin (ir-inhibin) levels and the relationship among ir-inhibin, gonadotropins and testosterone were examined in 53 Holstein bull calves from neonates to 8.6 months old. Serum levels of ir-inhibin, luteinizing hormone (LH), follicle stimulating hormone (FSH) and testosterone, as well as ir-inhibin levels in testicular extracts, and testicular sizes were measured. All hormones were measured by specific radioimmunoassays. The concentrations of ir-inhibin in serum and testicular tissue were high in neonatal calves and tended to decrease with age. In contrast, serum concentrations of gonadotropins did not show any age-related changes within the experimental period. Serum testosterone levels and testicular sizes (length, width and weight) were positively correlated with age. Furthermore, a positive immunostaining to antiserum for the inhibin alpha-subunit was immunocytochemically observed only in Sertoli cells of the seminiferous tubules from neonates to calves less than 6 months old. These results indicate that the immature bovine testis produces and secretes high levels of ir-inhibin and that the Sertoli cells are a major source of ir-inhibin in prepubertal bull calves.