1. Animal Science 434 Lecture 8: The Onset of Puberty

2. Development of Hypothalamus and GnRH Release Centers

3. Hypothalamus GnRH Control Centers in the Female Why does the male only have tonic control centers develop?

4. Male Brain Development Testis T TE2E2 Surge Center Does not Develop Surge Center Does not Develop Blood Brain Barrier

5. Female Brain Development Ovary E2E2 E2E2 E2E2 Placenta E2E2  FP + E 2 Surge Center Develops Surge Center Develops Blood Brain Barrier

7. Puberty The ability to accomplish reproduction successfully.

8. Puberty in the Female Age at first estrus (heat) Age at first ovulation Age at which the female can support pregnancy

9. Puberty in the Male Age when behavioral traits are expressed Age at first ejaculation Age when sperm first appear in the ejaculate Age when sperm first appear in the urine Age when the ejaculate contains a threshold number of sperm

10. Average Age of Puberty (Range) SpeciesMaleFemale Bovine11 mo (7-18)11 mo (9-24) Ovine7 mo (6-9)7 mo (4-14) Porcine7 mo (5-8)6 mo (5-7) Equine14 mo (10-24)18 mo (12-19) Human13 yr12 yr

11. Puberty Hormonal Nutritional Genetic Environment

12. Role of GnRH Pulses Hormonal

13. GnRH Pulses Determine Puberty Prepubertal period » minimal GnRH release » FSH and LH low » minimal to no folliculargenesis or spermatogenesis Puberty » increase in the pulse frequency and amplitude of GnRH release » increase in FSH and LH pulses » folliculargenesis and spermatogenesis occur

14. Hormonal Changes in the Female

15. Changes in GnRH Secretion With Puberty Surge Tonic Surge Tonic

16. Surge Tonic

17. Potential Regulators of GnRH Pulses at Puberty Development of surge center Change in the feedback sensitivity to estradiol

18. Development of the Hypothalamic GnRH Surge Center Positive Feedback is possible prior to puberty Puberty = 28 - 30 weeks

19. Negative Feedback Decreased Neg. Feedback Changes in Feeback Sensitivity to Estradiol

20. Puberty in the Female

21. Silent Ovulation at Puberty

22. Hormonal Changes in the Male

23. Puberty in the Stallion Puberty LH (ng/ml) FSH (ng/ml) Testosterone (ng/ml) LH FSH T T

24. Increased Gonadotropins Testosterone Remains Low Caused by GnRH Sertoli cells mature and multiply Spermatogonia begin to divide LH (ng/ml) FSH (ng/ml) Testosterone (ng/ml) LH FSH T T

25. Puberty Testosterone Increases Sperm found in the ejaculate FSH Increases LH (ng/ml) FSH (ng/ml) Testosterone (ng/ml) LH FSH T T

26. Genetics

27. Influence of Breed on Age of Puberty Average Age at Puberty (Months)

28. Nutrition

29. Availability of Energy Changes with Growth

30. Effect of 2-deoxyglucose on LH Pulses Decreased Amplitude and Frequency

31. Effect of Nutrition on Puberty

32. Dairy Cattle30-40% Beef cattle 55-65% Sheep40- 63% % Mature Weight at Puberty

33. Environmental and Social Conditions

34. Effect of the Number of Females Housed Together and Exposure to A Male

35. 28 Weeks 32 Weeks 24 Weeks

36. Influence of Growth Rate and Bull Exposure on Age of Puberty High Growth Rate Moderate Growth Rate High Growth Rate Moderate Growth Rate 0 100 200 300 400 500 Age at Puberty (days) Heifers only Bull Exposure 449 428 422 375

37. Puberty Hormonal Nutritional Genetic Environment

38. Recommended Age to Breed Heifer15 months (65% mature BW) Bull15 natural mating, 12 months AI Filly2-3 years Colt2 years Boar9 months