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
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