Animal Science 434 Reproductive Physiology Puberty Development of

Animal Science 434 Reproductive Physiology Puberty

Development of Hypothalamus and Gn. RH Release Centers Males and Females are Different!!!

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

Male Brain Development T Testis T Surge Center Does not Develop E 2 Blood Brain Barrier

Female Brain Development E 2 Placenta E 2 E 2 Ovary Blood Brain Barrier

Female Brain Development a. FP + E 2 Placenta E 2 E 2 Ovary Surge Center Develops Blood Brain Barrier

Fundamental Male and Female Differences Pulse Patterns Surge + Tonic

Puberty • • • The ability to accomplish reproduction. Definitions in Male and Female » See Textbook Age of Puberty

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 Female

Hypothalamic Secretion of Gn. RH Low Amplitude and Frequency Senger, 2012

Hypothalamic Secretion of Gn. RH Senger, 2012

Hypothalamic Secretion of Gn. RH Pattern!! Senger, 2012

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 Puberty = 28 - 30 weeks

Development of the Hypothalamic Gn. RH Surge Center Puberty = 28 - 30 weeks Positive Feedback is possible prior to puberty

Changes in Feedback Sensitivity to Estradiol Negative Feedback Decreased Neg. Feedback

Puberty in the Female

Silent Ovulation at Puberty

Steroid Hormone Influence on Gn. RH Neurons Estrogen and Progesterone receptors for negative feedback. Kisspeptin neurons - Gn. RH neuron - - + Kisspeptin neurons + + Estrogen receptor for positive feedback. Gn. RH neuron Gn. RH

Hormonal Changes in the Male

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 LH (ng/ml) Before 2 DG Gn. RH During 2 DG 3 2 1 0 1 2 3 4 5 6 7 Time (hours) 8 9 10 11

Effect of 2 -deoxyglucose on LH Pulses LH (ng/ml) Before 2 DG Gn. RH During 2 DG 3 2 1 0 1 2 3 4 5 6 7 Time (hours) 8 9 10 11 Decreased Amplitude and Frequency

Metabolic Signals Influence Gn. RH Neurons Glucose sensing Pre-pubertal or neurons Blood Glucose Starvation - - ? - Neuropeptide Y neurons Leptin Kisspeptin neurons - - ? Gn. RH neurons Gn. RH - - Fatty Acid sensing neurons Adipocytes (Fat) Kisspeptin neurons - - Blood Fatty Acids

Metabolic Signals Influence Gn. RH Neurons Glucose sensing + Post-pubertal neurons Blood Glucose + ? + + Neuropeptide Y neurons Leptin Kisspeptin neurons + + ? + + Gn. RH neurons Gn. RH + + Fatty Acid sensing neurons Adipocytes (Fat) Kisspeptin neurons + + Blood Fatty Acids

Effect of Nutrition on Puberty Body Weight (X 100 lbs. ) 12 1. 5 lb/day 2. 0 lb/day 10 8 Puber 6 ty 1. 2 lb/day 4 2 0 0 4 8 12 16 Age (months) 20 24

% 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 Moderate Growth Rate High Growth Rate 375 300 200 100 0 Heifers only Bull Exposure

Mechanism of Social Effects • • Pheromones Impacts on Gn. RH » Nasal receptors impact nerve tracts to the hypothalamus

Genetic Hormonal Puberty Environment Nutritional

Recommended Age to Breed • Heifer 15 months (65% mature BW) • Bull 15 natural mating, 12 months AI, 9 - 10 months IVF • Filly 2 -3 years • Colt 2 years (immature behavior until 3) • Gilt 8 – 9 months • Boar 9 months