Animal Science 434

Lecture 8: The Onset of Puberty

Development of

Hypothalamus and GnRH

Release Centers

Males and Females are Different!!!

Hypothalamus GnRH Control Centersin the Female

Why does the maleonly have tonic control

centers develop?

Male Brain Development

Testis

T

T E2

Surge CenterDoes notDevelop

Blood BrainBarrier

Female Brain Development

OvaryE2

E2 E2

PlacentaE2

Blood BrainBarrier

Female Brain Development

OvaryE2

E2 E2

PlacentaE2αFP + E2

Surge CenterDevelops Blood Brain

Barrier

Fundamental Male and Female Differences

Surge + TonicSurge + Tonic

TonicTonic

PulsePatterns Puberty

The ability to accomplishreproduction successfully.

Puberty in the Female

• Age at first estrus (heat)

• Age at first ovulation

• Age at which the female can supportpregnancy

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 thresholdnumber of sperm

Average Age of Puberty (Range)

Species Male FemaleBovine 11 mo (7-18) 11 mo (9-24)Ovine 7 mo (6-9) 7 mo (4-14)

Porcine 7 mo (5-8) 6 mo (5-7)Equine 14 mo (10-24) 18 mo (12-19)Human 13 yr 12 yrCanine 9 mo (5 - 12) 12 mo (6 - 24)

Feline 9 mo (8 - 10) 8 mo (4 -12)

Puberty

Hormonal

Nutritional

Genetic

Environment

Role of GnRH Pulses

Hormonal 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

Hormonal Changes in the Female

Changes in GnRH Secretion With Puberty

SurgeTonic

Low Amplitudeand FrequencyLow Amplitudeand Frequency

Changes in GnRH Secretion With Puberty

SurgeTonic

Changes in GnRH Secretion With Puberty

SurgeTonic Surge

Tonic

Surge

Tonic

Potential Regulators of GnRH Pulsesat Puberty

• Development of surge center• Change in the feedback sensitivity to

estradiol

Development ofthe

HypothalamicGnRH Surge

Center

Puberty =28 - 30 weeksPuberty =28 - 30 weeks

Development ofthe

HypothalamicGnRH Surge

Center

PositiveFeedback is

possible priorto puberty

PositiveFeedback is

possible priorto puberty

Puberty =28 - 30 weeksPuberty =28 - 30 weeks

Negative Feedback Decreased Neg. Feedback

Changes in Feeback Sensitivity to EstradiolPuberty in the Female

Silent Ovulation at Puberty

Hormonal Changes in the Male

Puberty in the Stallion

0

5

10

15

20

25

0 20 40 60 80 100

0

0.5

1

1.5

0 20 40 60 80 1000

2

4

6

8

0 20 40 60 80 100

Age (wk)

Puberty

LH (n

g/m

l)

FSH

(ng/

ml)

Testosterone (ng/ml)

LH

FSH

T0

5

10

15

20

25

0 20 40 60 80 100

0

0.5

1

1.5

0 20 40 60 80 1000

2

4

6

8

0 20 40 60 80 100

Age (wk)

Increased GonadotropinsCaused by GnRH

LH (n

g/m

l)LH

(ng/

ml)

FSH

(ng/

ml)

FSH

(ng/

ml)

Testosterone (ng/ml)

LH

FSHFSH

TT

0

5

10

15

20

25

0 20 40 60 80 100

0

0.5

1

1.5

0 20 40 60 80 1000

2

4

6

8

0 20 40 60 80 100

Age (wk)Testosterone Remains Low

• Sertoli cells mature and multiply• Spermatogonia begin to divide

LH (n

g/m

l)LH

(ng/

ml)

FSH

(ng/

ml)

FSH

(ng/

ml)

Testosterone (ng/ml)

LH

FSHFSH

TT0

5

10

15

20

25

0 20 40 60 80 100

0

0.5

1

1.5

0 20 40 60 80 1000

2

4

6

8

0 20 40 60 80 100

Age (wk)

Puberty

Testosterone Increases Sperm found inthe ejaculate

FSH Increases

LH (n

g/m

l)LH

(ng/

ml)

FSH

(ng/

ml)

FSH

(ng/

ml)

Testosterone (ng/ml)

LHLH

FSHFSH

TT

Genetics

Influence of Breed on Age of Puberty Species

Female Male Cattle

Holstein 8.5 9.0Brown Swiss 11.6 8.8Angus 12.4 9.8Hereford 13.0 10.8Brahman 19.0 17.0

Swine

Meishan 3.1 3.0Large White 6.3 5.8Yorkshire 7.0 6.5

Sheep

Rambouillet 9.2Finish Landrace 8.6

Average Age at Puberty (Months)

Nutrition

Availability of Energy Changes withGrowth

Effect of 2-deoxyglucose on LH Pulses

3

2

1

0 1 2 3 4 5 6 7 8 9 10 11Time (hours)

LH (n

g/m

l)

GnRHGnRHBefore 2DG During 2DG

Effect of 2-deoxyglucose on LH Pulses

Decreased Amplitude andFrequency

3

2

1

0 1 2 3 4 5 6 7 8 9 10 11Time (hours)

LH (n

g/m

l)

GnRHGnRHBefore 2DG During 2DG

Metabolic Signals Influence GnRH Neurons

GnRHGnRH

Adipocytes(Fat)

Leptin

Blood Glucose

GnRHneuronsGnRH

neurons

Glucose sensingneurons

Neuropeptide Yneurons

Blood Fatty Acids

?

?

Fatty Acidsensing neurons

Effect of Nutrition on Puberty12

10

8

6

4

2

00 4 8 12 16 20 24

Body

Wei

ght (

X 10

0 lb

s.)

Age (months)

Puberty

2.0 lb/day

1.2 lb/day

1.5 lb/day

Dairy Cattle 30-40%

Beef cattle 55-65%

Sheep 40- 63%

% Mature Weight at Puberty

Environmental and Social Conditions

Effect of the Number of FemalesHoused Together

andExposure to A Male

28 Weeks

32Weeks

24 Weeks

24 Weeks

Influence of Growth Rate and BullExposure on Age of Puberty

Moderate Growth RateHigh Growth Rate

0

100

200

300

400

500

Age

at P

uber

ty (d

ays)

Heifersonly

BullExposure

449 428 422375

Puberty

Hormonal

Nutritional

Genetic

Environment

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