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AN SC 312 > 6 - Estrous Cycle > Flashcards

6 - Estrous Cycle Flashcards

1
Q

Menstrual vs estrous cycle

A

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)

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2
Q

Estrus vs estrous

A

Estrus: period of sexual receptivity in a female (aka heat)

Estrous: describes a phenomena related to the reproductive cycle

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3
Q

Anestrus vs anestrous

A

Anestrus: period when a female does not exhibit an estrous cycle

Anestrous: describes a phenomena related to anestrus

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4
Q

What is “in season”

A

Period of reproductive activity in seasonal breeding females

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5
Q

Types of reproductive cyclicity

A

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

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6
Q

Two types of seasonal polyestrus animals

A

Short day breeders: autumn breeding season (e.g. sheep, goat)

Long day breeders: spring breeding season (e.g. mare)

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7
Q

Slides 8-10

A

types of cyclicity

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8
Q

Estrous cycles of cow, mare, bitch, ewe

A

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)

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9
Q

Two phases of estrous cycle, different stages in them

A

Follicular phase: proestrus and estrus

Luteal phase: metestrus and diestrus

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10
Q

What occurs in proestrus

A

P4 levels decline as CL regresses
GnRH released = LH and FSH secretion
Ovarian follicular development starts & tract prepares for mating
Estradiol secretion

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11
Q

What happens in the estrus stage

A

Estradiol secretion peaks
Receptivity to mating (standing heat)
Hypothalamus surge center triggered: peak GnRH release
LH surge induces ovulation

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12
Q

What happens in metestrus

A

CL forms from cells of ovulated follicle (luteinization)
P4 levels start to increase
E2 levels decrease

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13
Q

What happens in diestrus

A

P4 levels plateau
Uterus prepares to support embryonic development
Female unreceptive to mating
PGF2a from uterus causes regression of CL & prompts transition to proestrus

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14
Q

Slides 15-19

A

Important diagrams

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15
Q

What is anestrus

A

Period when a female does not exhibit an estrous cycle

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16
Q

Causes of anestrus (5)

A
  • Pregnancy (gestational anestrus)
  • Nursing (lactational anestrus)
  • Photoperiod (seasonal anestrus)
  • Nutritional status (nutritional anestrus)
  • Disease or infection (pathological anestrus)
17
Q

Why does gestational anestrus occur? Allows for…

A

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

18
Q

Why does lactational anestrus occur? Exceptions?

A

Most mammalian females lack estrus while nursing
Metabolic necessity - energy conservation
Exceptions: mare, bitch

19
Q

Factors that stimulate lactation anestrus (4)

A
  • mammary stimulation (suckling)
  • visual stimulation (offspring in view)
  • olfactory stimulation (offspring odour)
  • auditory stimulation (offspring vocalization)
20
Q

Why can dairy cows be bred during lactation?

A

Calf is removed; no offspring stimulating lactational anestrus

21
Q

Why did seasonal anestrus evolve

A

Enhance embryonic and neonatal survival (early gestation during moderate temperatures; parturition when nutrients available to lactating mother)

22
Q

How is seasonal anestrus controlled

A

Photoperiod
Hypothalamus exhibits GnRH “dormancy” during off-season

23
Q

Gland associated with seasonal anestrus

A

Pineal gland
Releases melatonin in response to dark which alters reproductive function

24
Q

Slide 26***

A

Seasonal breeders

25
Q

Why did nutritional anestrus evolve? Common in who?

A

Enhance maternal, embryonic and neonatal survival (poor nutritional status = decreased body fat = lack of GnRH production by hypothalamus)

Common in primiparous (1st lactation) females

26
Q

Examples of causes of pathological anestrus

A

Uterine infection, persistent CL, cystic ovaries, mummified fetus

AN SC 312 (31 decks)

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