Animal Science 434Lecture 8: The Onset of PubertyDevelopment ofHypothalamus and GnRH Release CentersMales and Females are Different!!!Hypothalamus GnRH Control Centersin the FemaleWhy does the maleonly have tonic control centers develop?Male Brain DevelopmentTestisTT E2Surge CenterDoes notDevelopBlood BrainBarrierFemale Brain DevelopmentOvaryE2E2E2PlacentaE2Blood BrainBarrierFemale Brain DevelopmentOvaryE2E2E2PlacentaE2αFP + E2Surge CenterDevelopsBlood BrainBarrierFundamental Male and Female DifferencesSurge + TonicSurge + TonicTonicTonicPulsePatternsPubertyThe ability to accomplishreproduction successfully.Puberty in the Female• Age at first estrus (heat)• Age at first ovulation• Age at which the female can supportpregnancyPuberty 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 spermAverage 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)PubertyHormonalNutritionalGeneticEnvironmentRole of GnRH PulsesHormonalGnRH 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 ofGnRH release» increase in FSH and LH pulses» folliculargenesis and spermatogenesis occurHormonal Changes in the FemaleChanges in GnRH Secretion With PubertySurgeTonicLow Amplitudeand FrequencyLow Amplitudeand FrequencyChanges in GnRH Secretion With PubertySurgeTonicChanges in GnRH Secretion With PubertySurgeTonicSurgeTonicSurgeTonicPotential Regulators of GnRH Pulsesat Puberty• Development of surge center• Change in the feedback sensitivity toestradiolDevelopment oftheHypothalamicGnRH SurgeCenterPuberty =28 - 30 weeksPuberty =28 - 30 weeksDevelopment oftheHypothalamicGnRH SurgeCenterPositiveFeedback ispossible priorto pubertyPositiveFeedback ispossible priorto pubertyPuberty =28 - 30 weeksPuberty =28 - 30 weeksNegative Feedback Decreased Neg. FeedbackChanges in Feeback Sensitivity to EstradiolPuberty in the FemaleSilent Ovulation at PubertyHormonal Changes in the MalePuberty in the Stallion05101520250 20 40 60 80 10000.511.50 20 40 60 80 100024680 20 40 60 80 100Age (wk)PubertyLH (ng/ml)FSH (ng/ml)Testosterone (ng/ml)LHFSHT05101520250 20 40 60 80 10000.511.50 20 40 60 80 100024680 20 40 60 80 100Age (wk)Increased GonadotropinsCaused by GnRHLH (ng/ml)LH (ng/ml)FSH (ng/ml)FSH (ng/ml)Testosterone (ng/ml)LHFSHFSHTT05101520250 20 40 60 80 10000.511.50 20 40 60 80 100024680 20 40 60 80 100Age (wk)Testosterone Remains Low• Sertoli cells mature and multiply• Spermatogonia begin to divideLH (ng/ml)LH (ng/ml)FSH (ng/ml)FSH (ng/ml)Testosterone (ng/ml)LHFSHFSHTT05101520250 20 40 60 80 10000.511.50 20 40 60 80 100024680 20 40 60 80 100Age (wk)PubertyTestosterone IncreasesSperm found inthe ejaculateFSH IncreasesLH (ng/ml)LH (ng/ml)FSH (ng/ml)FSH (ng/ml)Testosterone (ng/ml)LHLHFSHFSHTTGeneticsInfluence 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 8.6Average Age at Puberty (Months)NutritionAvailability of Energy Changes withGrowthEffect of 2-deoxyglucose on LH Pulses3210 1 2 3 4 5 6 7 8 9 10 11Time (hours)LH (ng/ml)GnRHGnRHBefore 2DG During 2DGEffect of 2-deoxyglucose on LH PulsesDecreased Amplitude andFrequency3210 1 2 3 4 5 6 7 8 9 10 11Time (hours)LH (ng/ml)GnRHGnRHBefore 2DG During 2DGMetabolic Signals Influence GnRH NeuronsGnRHGnRHAdipocytes(Fat)LeptinBlood GlucoseGnRHneuronsGnRHneuronsGlucose sensingneuronsNeuropeptide YneuronsBlood Fatty Acids??Fatty Acidsensing neuronsEffect of Nutrition on Puberty1210864200 4 8 12 16 20 24Body Weight (X 100 lbs.)Age (months)Puberty2.0 lb/day1.2 lb/day1.5 lb/dayDairy Cattle 30-40%Beef cattle 55-65%Sheep 40- 63%% Mature Weight at PubertyEnvironmental and Social ConditionsEffect of the Number of FemalesHoused TogetherandExposure to A Male28 Weeks32Weeks24 Weeks24 WeeksInfluence of Growth Rate and BullExposure on Age of PubertyModerate Growth RateHigh Growth Rate0100200300400500Age at Puberty (days)HeifersonlyBullExposure449428422375PubertyHormonalNutritionalGeneticEnvironment 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
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