Circulating Metabolic Hormones During the Peripubertal Period and Their Association with Testicular Development in Bulls

• Published in: Reproduction in domestic animals Vol. 42; no. 5; pp. 502 - 508
• Main Authors: Brito, LFC, Barth, AD, Rawlings, NC, Wilde, RE, Crews, DH Jr, Mir, PS, Kastelic, JP
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01.10.2007; Blackwell Publishing Ltd; Blackwell Science
• Subjects: Aging - blood; Aging - physiology; Animal reproduction; Animals; Biological and medical sciences; Cattle; Cattle - blood; Cattle - growth & development; Cattle - physiology; Follicle Stimulating Hormone - blood; Fundamental and applied biological sciences. Psychology; Gonadotropins - blood; Growth Hormone - blood; Hormones; Insulin - blood; Insulin-Like Growth Factor I - metabolism; Leptin - blood; Luteinizing Hormone - blood; Male; Males; Mammalian reproduction. General aspects; Puberty; Reproductive system; Scrotum - anatomy & histology; Scrotum - physiology; Sexual Development - physiology; Sexual Maturation - physiology; Testis - anatomy & histology; Testis - growth & development; Testis - physiology; Testosterone - secretion; Vertebrates: reproduction; Hormone; Puberty; Vertebrata; Mammalia; Development; Metabolism; Testicle; Male genital system
• ISSN: 0936-6768; 1439-0531
• DOI: 10.1111/j.1439-0531.2006.00813.x

The objective of the present study was to characterize changes in serum metabolic hormones concentrations from 20 weeks before to 20 weeks post-puberty in bulls and to investigate the associations of metabolic hormones concentrations with testicular development. Leptin concentrations increased from 16 weeks before puberty to 8 weeks post-puberty and insulin concentrations increased from puberty to 8 weeks post-puberty. Growth hormone concentrations decreased after 4 weeks post-puberty, whereas IGF-I concentrations increased from 8 weeks before puberty to 8 weeks post-puberty. During this period, testicular growth was accelerated and testosterone secretion increased substantially, without any significant changes in gonadotropin secretion. Monthly circulating concentrations of leptin, IGF-I and insulin accounted for 63% of the variation in scrotal circumference and 59% of the variation in paired testes volume. In conclusion, the secretion of metabolic hormones was not associated with changes in gonadotropins concentrations. Furthermore, the associations of leptin, IGF-I and insulin concentrations with testes size indicated that these hormones might be involved in a gonadotropin-independent mechanism regulating the testicular development in peripubertal bulls.