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

2. The ability to accomplish reproduction successfully.
Puberty
The ability to accomplish reproduction successfully.

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

4. 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

5. Average Age of Puberty (Range)

6. Hormonal
Genetic
Puberty
Environment
Nutritional

7. Hormonal
Role of GnRH Pulses

8. 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

9. Hormonal Changes in the Male

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

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

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

14. Hormonal Changes in the Female

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

17. Male Brain Development

18. Female Brain Development

19. Changes in LH Secretion With Puberty
Surge
Surge
Tonic
Tonic

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

21. Development of the Hypothalamic GnRH Surge Center

22. Development of Estradiol Positive Feedback
Age (weeks)

23. Development of Estradiol Positive Feedback

24. Development of Estradiol Positive Feedback
Negative Feedback
Positive Feedback

25. Puberty in the Female

26. Silent Ovulation at Puberty

27. Genetics

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

29. Nutrition

30. Availability of Energy Changes with Growth

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

32. Effect of Nutrition on Puberty

33. % Mature Weight at Puberty
Dairy Cattle 30-40%
Beef cattle %
Sheep %

34. Environmental and Social Conditions

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

36. 32
Weeks 28
Weeks
24 Weeks
24 Weeks

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

38. Hormonal
Genetic
Puberty
Environment
Nutritional

39. Recommended Age to Breed
Heifer 15 months (65% mature BW)
Bull 15 natural mating, 12 months AI
Filly 2-3 years
Colt 2 years
Boar 9 months

40. Lecture Exam 1 Includes:
lectures through tues (some points I have missed will be covered)
all handouts and lecture outlines
chapters 1-6 in text
exam format
multiple choice
true/false
short answer
one essay question on mechanism of hormone action (drawing a diagram will not be a suitable answer)