Animal Science 434

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Animal Science 434

• Lecture 8 The Onset of Puberty

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Development of Hypothalamus and GnRH Release
Centers
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Hypothalamus GnRH Control Centers in the Female
Why does the male only have tonic control
centers develop?
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Male Brain Development
T
Testis
T
E2
Surge Center Does not Develop
Blood Brain Barrier
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Female Brain Development
aFP E2
Placenta
E2
E2
E2
E2
Ovary
Surge Center Develops
Blood Brain Barrier
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Puberty

• The ability to accomplish reproduction
  successfully.

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Puberty in the Female

• Age at first estrus (heat)
• Age at first ovulation
• Age at which the female can support pregnancy

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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

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Average Age of Puberty (Range)
Species Male Female Bovine 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 yr
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Puberty
Genetic
Hormonal
Environment
Nutritional
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Role of GnRH Pulses
Hormonal
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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

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Hormonal Changes in the Female
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Changes in GnRH Secretion With Puberty
Surge
Surge
Tonic
Tonic
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Surge
Tonic
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Potential Regulators of GnRH Pulses at Puberty

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

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Development of the Hypothalamic GnRH Surge Center
Puberty 28 - 30 weeks
Positive Feedback is possible prior to puberty
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Changes in Feeback Sensitivity to Estradiol
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Puberty in the Female
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Silent Ovulation at Puberty
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Hormonal Changes in the Male
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Puberty in the Stallion
Puberty
FSH
LH (ng/ml)
FSH (ng/ml)
Testosterone (ng/ml)
LH
T
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FSH
LH (ng/ml)
FSH (ng/ml)
Testosterone (ng/ml)
LH
T
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FSH Increases
Puberty
FSH
LH (ng/ml)
FSH (ng/ml)
Testosterone (ng/ml)
LH
T
Sperm found in the ejaculate
Testosterone Increases
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Genetics
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Influence of Breed on Age of Puberty
Average Age at Puberty (Months)
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Nutrition
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Availability of Energy Changes with Growth
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Effect of 2-deoxyglucose on LH Pulses
Decreased Amplitude and Frequency
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Effect of Nutrition on Puberty
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Mature Weight at Puberty
Dairy Cattle 30-40 Beef cattle
55-65 Sheep 40- 63
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Environmental and Social Conditions
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Effect of the Number of Females Housed
TogetherandExposure to A Male
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32 Weeks
28 Weeks
24 Weeks
24 Weeks
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Influence of Growth Rate and Bull Exposure on Age
of Puberty
High Growth Rate Moderate Growth Rate
500
449
428
422
400
375
300
Age at Puberty (days)
200
100
0
Heifers only
Bull Exposure
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Puberty
Genetic
Hormonal
Environment
Nutritional
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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