Animal Science 434 Lecture 8 The Onset of
- Slides: 41
Animal Science 434 Lecture 8: The Onset of Puberty
Puberty The ability to accomplish reproduction successfully.
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 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)
Genetic Hormonal Puberty Environment Nutritional
Hormonal Role of Gn. RH Pulses
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
Puberty in the Stallion Puberty
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
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
Hypothalamus Gn. RH Control Centers in the Female Why does the male only have tonic control centers develop?
Male Brain Development
Female Brain Development
Changes in LH Secretion With Puberty Surge Tonic
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 Estradiol Positive Feedback 18 22 26 30 34 Age (weeks) 38 42
Development of Estradiol Positive Feedback
Development of Estradiol Positive Feedback Negative Feedback Positive Feedback
Puberty in the Female
Silent Ovulation at Puberty
Genetics
Influence of Breed on Age of Puberty Average Age at Puberty (Months)
Nutrition
Availability of Energy Changes with Growth
Effect of 2 -deoxyglucose on LH Pulses Decreased Amplitude and Frequency
Effect of Nutrition on Puberty
% Mature Weight at Puberty Dairy Cattle 30 -40% Beef cattle 55 -65% Sheep 40 - 63%
Environmental and Social Conditions
Effect of the Number of Females Housed Together and Exposure to A Male
32 Weeks 28 Weeks 24 Weeks
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
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 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)
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