Reproduction mid sem revision

• Puberty in females


  The attainment of maturity that allows a preovulatory surge of LH to occur in response to oestrogen (which is secreted by follicles in the ovary)
• Puberty attainment


  • The time of first oestrus
  • The age at first oestrus
  • The age at first ovulation
  • The age at which the female can support pregnancy
• Age of puberty attainment varies according to the species and breed
• Physiological basis of puberty


  1. Onset of puberty involves the hypothalamic pituitary ovarian axis

  2. Ovaries start to produce growing follicles

  3. The hypothalamus secretes increasing levels of GnRH

  4. GnRH acts on the pituitary gland which secretes FSH and LH

  5. This causes elevated ovarian activity
• Low levels of oestrogen


  Stimulates the development of secondary sex characteristics, but follicles do no ovulate at this stage
• Preovulatory LH surge


  Depends on the ability of the hypothalamic pituitary system to respond to oestrogen, some follicles become luteinized and secrete low levels of progesterone
• More FSH results


  More oestrogen release, increase in the LH surge
• The surge will eventually be sufficient enough to cause a normal ovulation, and the female has obtained puberty
• First ovulation


  A silent heat, as there is no prior exposure to progesterone
• Factors affecting the onset of puberty


  1. GnRH pulses determine puberty

  2. Body weight (40-60% mature weight)

  3. Season of birth

  4. Genetics

  5. Social factors

  6. Stress
• Prepubertal period


  Minimal GnRH release, FSH and LH are low, minimal to no folliculogenesis
• Puberty


  Increase in the pulse frequency and amplitude of GnRH release, increase in FSH and LH pulses, folliculogenesis occurs
• Larger breeds have a heavier weight requirement for puberty
• Factors that inhibit body growth also tend to inhibit the onset of puberty
• Non-seasonal animals depend on the availability of feed in order to reach puberty
• Prolific breeds


  Reach puberty at an earlier age and a lower proportion of mature weight
• Crossbreeding results in earlier puberty than the average parent
• Puberty is delayed in inbred females
• Sexual maturity


  Occurs when the animal reaches its full reproductive potential
• Younger females


  Have irregular oestrous cycles, lower ovulation rate, increased fertilisation failure, embryo loss, do not show intense behaviour patterns, do not seek or stand readily for the male, have shorter oestrus
• Only 40-60% of mature weight at puberty, pregnancy and lactation can place a large strain unless they are managed properly
• Poor management results in light birth weights, higher death rates, poor lactational performance, reduced weight at weaning
• Identification of puberty


  Need to identify females that are capable of breeding
• The longer you wait after puberty the better the performance will be
• Longer gestation lengths limit the ability to delay the breeding in some species
• Timing of breeding season also limits how late breeding can be delayed
• Sheep and goats are bred before June to avoid seasonal anoestrus, hoggests are mated 4-6 weeks after main flock
• Cattle occur soon after puberty due to longer post-partum anoestrus, heifers are mated 1-2 weeks earlier than main herd
• Advantages of breeding at a young age


  • Increase lifetime performance
  • Increase performance of total population within a given year
  • Allows detection of those predisposed to early breeding and potentially multiple births
  • Increases annual genetic gain
• Disadvantages of breeding at a young age


  • Being too small and under fed can have negative effects on lifetime performance
  • Variable reproductive performance
• Management of young females


  1. Only well grown females should be bred soon after puberty

  2. Join with an experienced male

  3. Use more 'male power' than used with mature females and use teams of males

  4. Use small flat paddocks

  5. Avoid competition from older more experienced females

  6. Ensure adequate nutrition during pregnancy and lactation

  7. Consider timing of breeding in relation to anoestrus period
• Mammary gland development


  Milk production has moderate to low heritability, but repeatability is high
• Mammary gland growth


  1. Foetal

  2. Prepubertal

  3. Postpubertal

  4. Pregnancy

  5. Lactation
• The size and development of the fat pad are important for mammary parenchymal tissue development
• Hormones and nutrition are critical for the mammary gland development
• Most of the major changes that occur before birth have occurred by mid-gestation
• At birth


  Teats are well developed, secondary sprouts are canalised, growth of the sprouts is limited to the area around the gland cistern, non-secretory tissue is well formed, secretory or glandular parts are not developed
• Sensitive period just prior to puberty


  Mammary gland undergoes a positive allometric growth spurt, growth of connective tissue, ductal growth and growth of the fat pad, formation of a duct network
• GH and leptin


  Required for prepubertal mammary development, secretion of GH is reduced in animals on a high plane of nutrition, systemic levels of leptin is increased in animals on elevated nutrition
• Rapid mammary growth continues through the first several oestrous cycles post puberty