Animal Science 434 Lecture 8 The Onset of

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Animal Science 434 Lecture 8: The Onset of Puberty

Animal Science 434 Lecture 8: The Onset of Puberty

Puberty The ability to accomplish reproduction successfully.

Puberty The ability to accomplish reproduction successfully.

Puberty in the Female • Age at first estrus (heat) • Age at first

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

Puberty in the Male • Age when behavioral traits are expressed • Age at

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

Average Age of Puberty (Range)

Average Age of Puberty (Range)

Genetic Hormonal Puberty Environment Nutritional

Genetic Hormonal Puberty Environment Nutritional

Hormonal Role of Gn. RH Pulses

Hormonal Role of Gn. RH Pulses

Gn. RH Pulses Determine Puberty • Prepubertal period – minimal Gn. RH release –

Gn. RH Pulses Determine Puberty • Prepubertal period – minimal Gn. RH release – FSH and LH low – minimal to no folliculargenesis or spermatogenesis • Puberty – increase in the pulse frequency and amplitude of Gn. RH release – increase in FSH and LH pulses – folliculargenesis and spermatogenesis occur

Hormonal Changes in the Male

Hormonal Changes in the Male

Puberty in the Stallion Puberty

Puberty in the Stallion Puberty

Increased Gonadotropins • Sertoli cells mature and multiply • Spermatogonia begin to divide Caused

Increased Gonadotropins • Sertoli cells mature and multiply • Spermatogonia begin to divide Caused by Gn. RH Testosterone Remains Low

FSH Increases Puberty Testosterone Increases Sperm found in the ejaculate

FSH Increases Puberty Testosterone Increases Sperm found in the ejaculate

Stimulates sperm production and testosterone from Ledig cells Bull Causes negative feedback which lowers

Stimulates sperm production and testosterone from Ledig cells Bull Causes negative feedback which lowers LH Spermatogonia start dividing Sperm in ejaculate

Hormonal Changes in the Female

Hormonal Changes in the Female

Hypothalamus Gn. RH Control Centers in the Female Why does the male only have

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

Male Brain Development

Male Brain Development

Female Brain Development

Female Brain Development

Changes in LH Secretion With Puberty Surge Tonic

Changes in LH Secretion With Puberty Surge Tonic

Potential Regulators of Gn. RH Pulses at Puberty • Development of surge center •

Potential Regulators of Gn. RH Pulses at Puberty • Development of surge center • Change in the feedback sensitivity to estradiol

Development of the Hypothalamic Gn. RH Surge Center

Development of the Hypothalamic Gn. RH Surge Center

Development of Estradiol Positive Feedback 18 22 26 30 34 Age (weeks) 38 42

Development of Estradiol Positive Feedback 18 22 26 30 34 Age (weeks) 38 42

Development of Estradiol Positive Feedback

Development of Estradiol Positive Feedback

Development of Estradiol Positive Feedback Negative Feedback Positive Feedback

Development of Estradiol Positive Feedback Negative Feedback Positive Feedback

Puberty in the Female

Puberty in the Female

Silent Ovulation at Puberty

Silent Ovulation at Puberty

Genetics

Genetics

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

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

Nutrition

Nutrition

Availability of Energy Changes with Growth

Availability of Energy Changes with Growth

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

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

Effect of Nutrition on Puberty

Effect of Nutrition on Puberty

% Mature Weight at Puberty Dairy Cattle 30 -40% Beef cattle 55 -65% Sheep

% Mature Weight at Puberty Dairy Cattle 30 -40% Beef cattle 55 -65% Sheep 40 - 63%

Environmental and Social Conditions

Environmental and Social Conditions

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

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

32 Weeks 28 Weeks 24 Weeks

32 Weeks 28 Weeks 24 Weeks

Age at Puberty (days) Influence of Growth Rate and Bull Exposure on Age of

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

Genetic Hormonal Puberty Environment Nutritional

Genetic Hormonal Puberty Environment Nutritional

Recommended Age to Breed • Heifer 15 months (65% mature BW) • Bull 15

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

Lecture Exam 1 Includes: • lectures up to this point • all handouts and

Lecture Exam 1 Includes: • lectures up to this point • all handouts and lecture outlines • chapters 1 -6 in text (even if not covered in lecture) • 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)