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Livestock Reproduction 333 > Estrus Cycle > Flashcards

Estrus Cycle Flashcards

1
Q

Describe the estrous cycle.

A

Period of time from one estrus to the next

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2
Q

What two phases make up the estrous cycle?

A

The follicular (regression of CL to ovulation) and luteal (ovulation to regression of CL) phase

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3
Q

What are the dominant structures during each phase of estrus?

A

Preovulatory follicles produce E2 during follicular phase

CL produces P4 during the luteal

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4
Q

Name the four stages of the estrus cycle.

A

Proestrus, estrus, metestrus and diestrus

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5
Q

What is it called when the female will arch her back for mating?

A

Lordosis

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6
Q

Name each species and the length of their estrous cycle.

A

Cow-18-24 days
Sheep- 14-19 days
Sow-18-22 days
Horse-16-24 days

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7
Q

Length of Estrus for each animal

A

Cow-12-19 hours
Sheep-24-36 hours
Sow-48-72 hours
Mare- 2-11 days

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8
Q

What is the longest stage of the estrus cycle?

A

Diestrus at 10-14 days

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9
Q

What are the different types of Anestrus?

A

Seasonal, Nutritional, Lactational, Gestational

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10
Q

What makes up the tonic GnRH center?

A

ME, ARC and VMN

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11
Q

What makes up the surge center?

A

PON, AHA, SCN

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12
Q

What life events can pause the estrous cycle?

A

Pregnancy, Lactation, season, inadequate nutrition and environmental

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13
Q

What is the difference between polyestrous and seasonally polyestrous?

A

Polestrous- Regular cycles through the year, cattle and swine

Seasonally- cycles that occur only a certain season of the year, sheep and horse

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14
Q

What stages of the estrous cycle are included in the follicular phase?

A

Proestrus and estrus

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15
Q

What stages of the estrous cycle are included in the luteal phase?

A

Metestrus and Diestrus

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16
Q

Describe the Proestrus phase.

A

Begins: P4 declines at lueolysis
Ends: Onset of estrus
2-5 days
Characterized by a transition from P4 and E2.

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17
Q

Describe Estrus.

A

Begins-When the female will stand to be mounted
End-When female no longer stands to be mounted
E2 induces the behaviors

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18
Q

Describe Metestrus.

A

Begin: Ovulation
End: Formation of the CL
2-5 days

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19
Q

Describe Diestrus.

A

When CL is functional and P4 is highest. 10-14 days

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20
Q

What is the main reason for all anesrus?

A

Insufficient release of GnRH

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21
Q

Gestational anestrus occurs when?

A

Due to elevated P4 from the CL and Placenta which decreases GnRH

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22
Q

Describe Silent Ovulation

A

When the female ovulates after a phase of anestrus without estrus

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23
Q

Why don’t dairy cattle experience lactational anestrus?

A

It suggests that the presence of the calf may be necessary

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24
Q

Describe the nutritional anestrus.

A

absence of GNRH pulses and inactive ovaries

It will prolong lactational anestrus

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25
Q

What are the four significant events that take place during follicular phase.

A
  • Ovulation
  • Sexual Receptivity
  • Follicular preparation for ovulation
  • Gonadotropin release from the AP
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26
Q

What is the appropriate stimulus for the the preovulatory to stop releasing basal levels of GnRH?

A

Its the threshold level of E2 in the absence of P4

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27
Q

Why does each of the GnRH pulses occur in the tonic center?

A

Due to simultaneous depolarizations of several GnRH neurons

28
Q

What does GnRH do?

A

Stimulates the release of FSH and LH from the AP causes the growth and development of the ovarian follicles

29
Q

Describe diestrus at a hormonal level.

A

P4 is high and E2 is low

30
Q

What is the difference between spontaneous and induced ovulators?

A

Spontaneous- ovulate with regular frequency and don’t require copulation. Cow, Sow, Horse, Ewe, Human
Induced- Require vagina stimulation and or cervix. Rabbit, Cats, Ferret

31
Q

What is tactile stimulation?

A

associated with copulation and is converted into action potentials that go from repro to the spinal cord and finally the hypothalamus

32
Q

What is required for hormonally induced ovulation?

A

Premature or controlled luteolysis

33
Q

How can premature or controlled luteolysis be accomplished?

A

administration of PGF2a

34
Q

How can progestational compounds be administered and what accompanies it?

A

Can be placed as a small capsule in the ear, an example is norgestamet.
Usually administered with a shot of E2.

35
Q

When hormonally controlling the ovulation what does E2 and norgestamet do?

A

E2-induces luteolysis

Norgestamet- Prevents estrus and ovulation

36
Q

What happens when the norgestamet is removed?

A

It mimics luteolysis and ovulation is induced

37
Q

What is MGA?

A

A progestagen that can be fed and withdraw

38
Q

When does the luteal phase last?

A

Time of ovulation-luteolysis and includes metestrus and diestrus

39
Q

When is the maximum P4 production the CL reached?

A

Diestrus

40
Q

What happens when the CL is lysed?

A

Becomes a corpus albicans

41
Q

What happens to the theca interna and grulosa cells after ovulation?

A

They become luteinized

42
Q

Why can’t the horses CL be palpated?

A

Because they are on the inside of the ovary

43
Q

What does the luteal tissue consist of and where do they originate?

A

Large cells- granulosa cells

Small cells- theca interna

44
Q

What do the large luteal cells in ruminants have?

A

The have dense secretory granules and they contain oxytocin during estrus and relaxin in pregnancy

45
Q

Do small luteal cells contain granules?

A

No

46
Q

Are both large and small luteal cells steriodogenic?

A

Yes

47
Q

What are the target organs for P4?

A

Hypothalamus, uterus and mammary gland

48
Q

P4 reduces the contractions in what species?

A

Ewe, Sow, Cow

49
Q

What affect does P4 have on the mammary glands?

A

Final alveolar development

50
Q

What feedback does P4 exert on the hypothalamus? And what does it do?

A

Exerts a strong negative feedback

Reduces the frequency of basal secretion of GnRH

51
Q

What behavior does P4 inhibit?

A

Inhibits estrual behavior and provide a positive priming effect on the brain

52
Q

What characterizes Luteolsis?

A

Dramatic drop in blood levels

53
Q

What two hormones control luteolysis? And what are they produced by?

A

Oxytocin produced by the CL

PGF2a produced by the endometrium

54
Q

Uterectomy prolongs the life of what?

A

The CL

55
Q

What is responsible for luteolysis ?

A

The uterus and is must physically be near the ovary

56
Q

Describe the tranportation process of PGF2a.

A

From the uterus it is carried to the ipsilateral ovary through the vascular countercurrent exchange mechanism

57
Q

Describe the countercurrent exchange system during the lysis of the Cl.

A

Two blood vessels where blood flows in opposite directions of the adjacent vessel

58
Q

What allows for PGF2a to be delivered in high concentrations?

A

PGF2a from the endometrium enters the uterine vein by the counter-currant exchange diffuses into the uterine vein.

59
Q

How much of the PGF2a is denatured in the lungs of the cow and the sow?

A

98-99% in the cow

40% in the sow

60
Q

What species does the countercurrent system present in?

A

Cow Sow and Ewe

Not the Mare because it doesn’t metabolize PGF2a to the same extent

61
Q

Describe the PG secretion cycle from the endometrium.

A

First half of the estrus cycle is is nonexistent.

During late luteal phase it is secreted in pulses

62
Q

Describe Phagocytic cells and give some examples

A

The produce intercellular mediators of the immune response called cytokines. Examples-TNF, interleukins, interferons

63
Q

What causes a local ischemia on the the CL.

A

PGF2a

64
Q

What will happen if we inject an animal during the late luteal phase?

A

Leads to rapid release of ovarian oxytocin which leads to the secretion of PGF2a

65
Q

What is the relationship of oxytocin and PGF2a?

A

Stimulate each other in a positive feedback

66
Q

How does P4 prevent the secretion of PGF2a?

A

Formation of oxytocin receptors

Livestock Reproduction 333 (16 decks)

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