Reproduction 2

• Puberty

  Period when an animal becomes fertile and manifests sexual behaviour which facilitates successful fertilization
• Sexual maturity


  The time of attainment of maximal reproductive potential
• Puberty and sexual maturity are not the same event and do not occur at the same time
• Onset of puberty


  • Depends on the ability of specific hypothalamic neurons to produce GnRH in sufficient quantities to promote and support gametogenesis

  
• Factors affecting the onset of puberty

  • Hormonal
  • Nutritional
  • Genetic
  • Environmental
• Hormonal factors affecting onset of puberty

  1. Pre-pubertal period: Minimal GnRH release, FSH and LH low, minimal to no folliculogenesis or spermatogenesis

  2. Puberty: Increase in pulse frequency and amplitude of GnRH, increase in FSH and LH pulses, folliculogenesis and spermatogenesis occur

  
• Nutritional factors affecting onset of puberty

  Critical stage of somatic development (adipose tissue) required, females normally attain threshold body mass before males, overfeeding leads to earlier onset, underfeeding leads to delayed onset

  
• Genetic factors affecting onset of puberty


  Different breeds attain puberty at different times, inbreeding delays onset, crossbreeding leads to intermediate time
• Environmental factors affecting onset of puberty

  Photoperiod, stress (infection, temperature, high humidity) delay onset, presence of adult males (sheep, pigs, cattle) shortens time of onset
• Testosterone in males


  Can be converted to DHT or estradiol in some target tissues
• Reproductive behaviours in males

  • Erection
  • Ejaculation
  • Intromission
  • Aggression
• Reproductive behaviours in females

  • Courtship
  • Libido
  • Mounting
  • Libido, sexual receptivity and estrous behaviour are cyclic due to estrogen after progesterone priming
  • Libido in primates with menstrual cycles due to adrenal androgens

  
• Average age of puberty varies between different species
• 
  

  steps in puberty onset

  1.hypothalamic secretion of GnRH increases

  2.gonadal maturation

  3.increase in gonadal hormones

  4.other pubertal changes
• what happens in pre-pubertal stage 


  hypothalamus does not secret sufficient GnRH (low frequency GnRH pulses)

  high hypothalamic sensitivity to estradiol negative feedback
• pubertal changes

  hypothalamus has decreased sensitivity to gonadal estradiol

  hypothalamus releases GnRH in high frequency pulses and amplitude

  increased LH and FSH release which initiates follicular growth and LH surge in females

  or initiation of spermatogenesis in males
• what is most important in reaching puberty

  reaching the right body weight and having enough leptin stores ,white adipocytes secret leptin
• average age of puberty in different species

  bovine M-11 months (7-18)F-1 year

  canine M-9mo(5-12) F-12mo (6-24)

  equine M-14mo (10-24) F-18 mo (12-19)

  porcine M-7mo (6-9) F -6mo (5-7)

  feline M-9 mo (8-10) F - 8mo (4-12)