Estrous Cycle
& Oogenesis
Animal Breeding
Pensacola Jr College
Definitions
w Estrous = the cycle of
changes in ovarian and hormonal condition from one estrus period to the next
w Estrus = Period when female
is receptive to the male and allows mating
Estrus Patterns
w Monestrus = one period of
estrus per year
w Seasonally polyestrus =
series of estrous cycles limited to a portion of year
w Polyestrus = Estrous cycles
are continuous throughout year
Puberty
w Age at first expressed
estrus with ovulation
Periods of Estrous
Cycle
w Estrus
w Metestrus
w Diestrus
w Proestrus
1. Estrus
w Female is receptive to male
w Ovulation in some species
w GnRH pulses à LH/FSH surge à estrogen surge
w Estrogen causes:
• Stand for mating, lordosis
• Response to male pheromones
• Restlessness, vocalizations
etc
2. Metestrus
w Formation of corpus luteum
w Ovulation in some species
w Metestrus bleeding in some
species
w LH high, prolactin surge
increases LH receptors
3. Diestrus
w Corpus luteum fully
functional
w Uterus prepares for
pregnancy
w Progesterone high
w Low waves of FSH/estrogen
allows selection and early development of follicles
4. Proestrus
w Regression of CL & rapid
follicle growth
w No pregnancy, prostaglandin
from uterus triggers CL regression in ovary
w Progesterone drops à stop negative feedback à waves of GnRH pulses à slow increase in estrogen
Oogenesis
w Formation and maturation of
female gametes (sex cell, egg)
w Primary oocytes before birth
w Oocyte grows and zona
pellucida (jelly coat) forms
w
Meiosis occurs
Cell Division (mitosis)
w Prophase = chromosomes
condense
w Metaphase = line up
w Anaphase = chromatids split
and move to opposite poles
w Telophase = nuclei form
w Result = 2 identical diploid
daughter cells
Prophase
Metaphase
Anaphase
Telophase
Cell Division
(meiosis)
w Prophase I= condense
w Metaphase I= SISTER
chromosomes line up
w Anaphase I= move to poles
w Telophase I= get 2 haploid
daughter cells, not the same
Meiosis (cont’d)
w Prophase II
w Metaphase II (note: often
arrested here to fertilization)
w Anaphase II
w Telophase II
w Above all identical to
mitosis
w End result of meiosis = 4
haploid daughter cells
Meiosis
Oogenesis
Ovulation types
w Spontaneous ovulators
• Animals that ovulate at a
specified point in the estrus cycle without required mating
w Induced ovulators
• Animals that only ovulate
when induced by copulation (mating)
Ovulation - Review
w Graafian follicle ovulates
w Ovulation trigger is surges
of FSH / estrogen
w Ovulation occurs during
estrus or metestrus
w Ovulated egg is surrounded
by zona pellucida, corona, and cumulus cells