title: Gonadotrophin secretion in prepubertal bull calves born in spring and autumn.
abstract: The reproductive development of bull calves born in spring and autumn was compared. Mean serum LH concentrations in calves born in spring increased from week 4 to week 18 after birth and decreased by week 24. In bull calves born in autumn, mean LH concentrations increased from week 4 to week 8 after birth and remained steady until week 44. LH pulse amplitude was lower in bull calves born in autumn than in calves born in spring until week 24 of age (P < 0.05). There was a negative correlation between LH pulse frequency at week 12 after birth and age at puberty in bull calves, irrespective of season of birth, and LH pulse frequency at week 18 also tended to correlate negatively with age at puberty. Mean serum FSH concentrations, age at puberty, bodyweight, scrotal circumference, testes, prostate and vesicular gland dimensions, and ultrasonographic grey scale (pixel units) were not significantly different between bull calves born in autumn and spring. However, age and body-weight at puberty were more variable for bull calves born in autumn (P < 0.05). In a second study, bull calves born in spring received either a melatonin or sham implant immediately after birth and at weeks 6 and 11 after birth. Implants were removed at week 20. Mean LH concentrations, LH pulse frequency and amplitude, mean FSH concentrations and age at puberty did not differ between the two groups. No significant differences between groups in the growth and pixel units of the reproductive tract were observed by ultrasonography. In conclusion, although there were differences in the pattern of LH secretion in the prepubertal period between bull calves born in autumn and spring, the postnatal changes in gonadotrophin secretion were not disrupted by melatonin treatment in bull calves born in spring. Reproductive tract development did not differ between calves born in spring and autumn but age at puberty was more variable in bull calves born in autumn. LH pulse frequency during the early prepubertal period may be a vital factor in determining the age of bull calves at puberty.
authors.affiliation: Department of Veterinary Physiological Sciences, University of Saskatchewan, Saskatoon, SK, S7N 5B4, Canada.
authors.forename: J P
authors.initials: JP
authors.lastname: Aravindakshan
authors.forename: A
authors.initials: A
authors.lastname: Honaramooz
authors.forename: P M
authors.initials: PM
authors.lastname: Bartlewski
authors.forename: A P
authors.initials: AP
authors.lastname: Beard
authors.forename: R R
authors.initials: RR
authors.lastname: Pierson
authors.forename: N C
authors.initials: NC
authors.lastname: Rawlings
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001835:Body Weight; D002417:Cattle / Q000502:physiology*; D005640:Follicle Stimulating Hormone / Q000097:blood / Q000378:metabolism; D006065:Gonadotropins, Pituitary / Q000378:metabolism*; D007091:Image Processing, Computer-Assisted; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism; D008297:Male; D008550:Melatonin / Q000494:pharmacology; D011467:Prostate / Q000000981:diagnostic imaging; D012621:Seasons; D012636:Secretory Rate / Q000502:physiology; D012741:Sexual Maturation / Q000187:drug effects / Q000502:physiology*; D013737:Testis / Q000000981:diagnostic imaging; D013739:Testosterone / Q000097:blood; D014463:Ultrasonography
chemical_list: D006065:Gonadotropins, Pituitary; D013739:Testosterone; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D008550:Melatonin