Estrous Cycle Flashcards
Estrus
heat
period of time when the female is sexualy receptive
standing heat= period of time when the female stands to be mated
Monoesterous
one estrous cycle per year
wolves, foxes, bears and dogs
Polyestrous
repeated estrous cycles are uniformly distributed throughout the year
cattle, swine, rodents
seasonally polyestrous
repeated estrous cycles for a portion of the year
horses, sheep, goats and cats
Diestrus
period of sexual quiescence separating phases of the estrous cycle in polyestrous animals
characterized by the activity of the CL which produces progesterone
Anestrus
period when female does not exhibit estrous cycles
ovaries are relatively inactive: no preovulatory follicles or CL
what causes anestrus
season, lactation, presence of offspring, pregnancy, stress and disease
Hormones
estrus- estrogen
diestrus- progesterone
anestrus-none?
Day 0 of estrus cycle
the estrous cycle begins and ends with estrus and/or ovulation
day of ovulation, or first day of estrus (species variations)
estrous cycle events
ovarian and behavioral
Ovarian events
follicular phase and luteal phase
Follicular phase
follicles are the dominant ovarian structure
20% of the estrous cycle
primary reproductive hormone is estradiol (E2)
Luteal phase
period from ovulation until CL regression
80% of the estrous cycle
primary reproductive hormone is progesterone (P4)
PGF 2a
causes progesterone to decrease and luteolysis to occur
Bovine estrous cycle phases
proestrus
estrus
metestrus
diestrus
Proestrus
early follicular phase
female attracts male but does not allow mating
Estrus
follicular phase
period of sexual receptivity and mating
Metestrus
early luteal phase
female is no longer receptive
Diestrus
luteal phase
the female refuses the male
Mare estrous cycle
2 stages only, estrus and diestrus
endocrine events
proestrus- transition from progesterone dominance to estrogen dominance
estrus- estrogens
metestrus- transition from estrogen dominance to progesterone dominance
diestrus- period of maximum luteal function (progesterone)
Estrogen
positive feedback on surge center in hypothalamus
negative feedback on anterior pituitary (LH and FSH)
inhibin
negative feedback on anterior pituitary (LH and FSH), to decrease FSH secretion
released by follicle
GnRH
produce in hypothalamus
acts on the pituitary to release FSH and LH
FSH
released from the anterior pituitary
acts on the ovary to produce follicles
Estradiol (E2)
released by the follicle, acts on brain to produce estrous behavior
triggers LH release presence of low P4 (+ feedback)
LH
luteinizing hormone, formation of the CL
released from anterior pituitary, selection and maturation of follicles
LH surge to induce ovulation
LH surge
occurs at day 0/estrus
Induced ovulator
camelid and queen (cat)
copulation necessary for ovulation
Luteal phase
P4 and prostaglandin
Progesterone
P4
secreted by CL, responsible for maintaining pregnancy
inhibits release of LH
Prostaglandin F2a
released by myometrium, lyses the CL (luteolysis)
progesterone falls and animal returns to estrus
types of cyclicity
Polyestrous, seasonally polyestrous and monestrous
Photoperiod
amount of daylight controls when animal will cycle
lack daylight increases melatonin secretion by pineal gland
melatonin acts on hypothalamus to either increase or decrease report hormones
short day breeders will cycle during fall/winter (ewe, doe)
long day breeders will not cycle during fall/winter (mare)
Short day breeder
decreased light, increase melatonin and increase ovarian activity
increased melatonin increases GnRH-cyclicity
with increased daylight decrease GnRH
Long day breeder
decreased light, increase melatonin, and decrease ovarian activity, decrease GnRH secretion-anestrus
with increased daylight increase GnRH
Estrous cycle summary
physiologic events that occur between successive periods of sexual receptivity (estrus or heat) and/or ovulation
2-4 stages, spontaneous and induced ovulates
cyclicality of some females is affected by the amount of daylight
