Summary: Reproduction And Fertility

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• 4 Puberty

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• when has a male of female reached puberty and what does it contain?

  when its able to release gametes and to manifest complete sexual behavioural sequences
  

  • Females mammals: the age at which first oestrus (excluding primates) with ovulation occurs, followed (in non-pregnant mammals) by regular cycles
  • Male vertebrates: the age at which the animal can produce an ejaculate with fertile sperm cells

• what is the function of the pituitary gland, steroids and gametes in males/females by puberty

  • Pituitary gland: producing LH and FSH
  • Steroids: in females = oestrogens, in males = testosterone
  • Gametes: in females = oocytes, in males = sperm cells

• what is causing the onset of puberty?

  stepwise desensibilisation of the hypothalamus for the negative feedback of the circulating seks steroids --> the hypothalamus becomes less sensitive to this negative feedback.
  

  • Causes a rise of GnRH / LH / FSH / seks steroids

• By the onset of puberty the pituitary becomes more responsive to GnRH. this results in:

  • Higher levels of gonadotropins
  • • increase as a result of an increase in both the amplitude and frequency of the pulses of gonadotropins
    • Results in oestrus with ovulation/oocytes and ejaculation of fertile sperm cells
  • Higher levels of sex steroids

• what is the cyclical pattern of females and males?

  • Females: cyclical pattern, resulting in periodic oestrogen (oestradial E2) peak -> Induce an LH surge (golf) --> ovulation
  • Males: dont have the cyclical pattern

• what causes the differences between male and female in prenatal development?

  • Fetal ovaries (females): produce oestrogens (E2) that bound to alpha-fetoprotein, which prevents them from entering the brain. 
  • Fetal testicles (males):  produce testosterone (T), can not bound to alpha-fetoprotein -> testosterone freely enters the brain -> is there converted into estradiol (defeminises the brain) -> males do not develop an GnRH surge centre after puberty

• Age of first oestrus of rabbits, sheep/goat/pig, cattle, horses is:

  
  Rabbit
  3-4 months
  Sheep, goat, pig
   6-7 months
  Cattle
  11-12 months
  Horses
  15-18 months

• what influences age at first oestrus?

  • Insemination
  • • Sheep at puberty
    • Cattle 15 months because it is more economically beneficial:
    • • less calving dificulties, higher milk production, longer lifespan
    • Pigs 7-8 months, more economically beneficial:
    • • lower weight loss during first lactation, improved reproductive performance after first lactation, longer lifespan
  • Age is genetically determined: differences in age at first oestrus betweens breeds of species
  • Influenced by the environment
  • • Physical environment, light, temperature, nutrition
  • Genotype-environment interaction: the influence of a certain environmental parameter does not affect all genotypes similarly

• why is nutrition important for puberty?

  Suboptimal nutrition extends the pre-pubertal phase. 
  

  • Puberty can not take place until the animal has reached a certain physiological development or body weight
  • In contrast to cattle, age at pubery in pigs is more influenced by age and less by feeding level and growth rate

• what are seasonal factors?

  Influence of ambient temperature and hours light per day
  

  • Short day breeders: sheep, feral pig
  • Long day breeders: horses
  • • Young in the spring: environmental temperature and food availability ensure high survival chances for their offspring