6 - Estrous Cycle Flashcards
Menstrual vs estrous cycle
Estrous cycle - period from one estrus (standing heat) to the next (reproductive cycle on non-primate females)
Menstrual cycle - period from one menstruation to the next (reproductive cycle of primate females)
Estrus vs estrous
Estrus: period of sexual receptivity in a female (aka heat)
Estrous: describes a phenomena related to the reproductive cycle
Anestrus vs anestrous
Anestrus: period when a female does not exhibit an estrous cycle
Anestrous: describes a phenomena related to anestrus
What is “in season”
Period of reproductive activity in seasonal breeding females
Types of reproductive cyclicity
Polyestrus: uniform distribution of estrous cycles throughout the year
Seasonal polyestrus: estrous cycles occur only during a certain period (season) of the year
Seasonal monoestrus: one estrous cycle per year
Two types of seasonal polyestrus animals
Short day breeders: autumn breeding season (e.g. sheep, goat)
Long day breeders: spring breeding season (e.g. mare)
Slides 8-10
types of cyclicity
Estrous cycles of cow, mare, bitch, ewe
Cow: 21 day cycle, 15 hour estrus (polyestrus)
Mare: 21 day cycle, 7 day heat (seasonal polyestrus)
Bitch: 6 month cycle, 9 day estrus (“monoestrus”)
Ewe: 17 day cycle, 30 hour heat (seasonal polyestrus)
Two phases of estrous cycle, different stages in them
Follicular phase: proestrus and estrus
Luteal phase: metestrus and diestrus
What occurs in proestrus
P4 levels decline as CL regresses
GnRH released = LH and FSH secretion
Ovarian follicular development starts & tract prepares for mating
Estradiol secretion
What happens in the estrus stage
Estradiol secretion peaks
Receptivity to mating (standing heat)
Hypothalamus surge center triggered: peak GnRH release
LH surge induces ovulation
What happens in metestrus
CL forms from cells of ovulated follicle (luteinization)
P4 levels start to increase
E2 levels decrease
What happens in diestrus
P4 levels plateau
Uterus prepares to support embryonic development
Female unreceptive to mating
PGF2a from uterus causes regression of CL & prompts transition to proestrus
Slides 15-19
Important diagrams
What is anestrus
Period when a female does not exhibit an estrous cycle
Causes of anestrus (5)
- Pregnancy (gestational anestrus)
- Nursing (lactational anestrus)
- Photoperiod (seasonal anestrus)
- Nutritional status (nutritional anestrus)
- Disease or infection (pathological anestrus)
Why does gestational anestrus occur? Allows for…
Lack of cyclicity = 1st indication of pregnancy
P4 from CL/placenta inhibits GnRH = FSH and LH release
Allows for embryonic/fetal development & uterine recovery post-partum
Why does lactational anestrus occur? Exceptions?
Most mammalian females lack estrus while nursing
Metabolic necessity - energy conservation
Exceptions: mare, bitch
Factors that stimulate lactation anestrus (4)
- mammary stimulation (suckling)
- visual stimulation (offspring in view)
- olfactory stimulation (offspring odour)
- auditory stimulation (offspring vocalization)
Why can dairy cows be bred during lactation?
Calf is removed; no offspring stimulating lactational anestrus
Why did seasonal anestrus evolve
Enhance embryonic and neonatal survival (early gestation during moderate temperatures; parturition when nutrients available to lactating mother)
How is seasonal anestrus controlled
Photoperiod
Hypothalamus exhibits GnRH “dormancy” during off-season
Gland associated with seasonal anestrus
Pineal gland
Releases melatonin in response to dark which alters reproductive function
Slide 26***
Seasonal breeders
Why did nutritional anestrus evolve? Common in who?
Enhance maternal, embryonic and neonatal survival (poor nutritional status = decreased body fat = lack of GnRH production by hypothalamus)
Common in primiparous (1st lactation) females
Examples of causes of pathological anestrus
Uterine infection, persistent CL, cystic ovaries, mummified fetus
