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Endocrine/Repro > Cyclicity and Seasonality > Flashcards

Cyclicity and Seasonality Flashcards

1
Q

when does cyclicity begin and end in a female?

A

begins at puberty once the female has reached 60-70% of her adult body weight

ends when the female runs out of primordial follicles

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2
Q

what interrupts estrous cycles, which are displayed from puberty to senescence? (3)

A
  1. seasonal (seasonal species only)
  2. pregnancy
  3. lactation
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3
Q

what is the goal of seasonality?

A

to give birth when weather conditions are optimal and food is abundant

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4
Q

give 4 seasonal and 4 non-seasonal species

A

seasonal: horses (long day), cats (long day), sheep (short day), goats (short day)

non-seasonal: pigs, cows, dogs, alpacas

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5
Q

how do seasonal breeders sync their fertile period with the appropriate season? (3)

A

environmental cues!

  1. photoperiod! at least 16 hour sunlight for long day, at least 16 hour no sun for short day)
  2. temperature
  3. nutrition

photoperiod is the main cue; determines season, temperature and nutrition fine-tune the week/day of fertility

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6
Q

describe the winter anestrus in the mare (4)

A
  1. the pineal glands serves as an extra, higher level of gonadotropin control above the hypothalamus; secretes melatonin during darkness
  2. in mares, melatonin inhibits GnRH secretion from hypothalamus (activates it in short day breeders)
  3. no GnRH = no FSH and LH
  4. no FSH and LH = no follicular growth or ovulation, meaning no estrogen production and no estrous behavior
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7
Q

describe spring transition in the mare (6)

A
  1. light detected by photoreceptors in the retina, travels to brain via sympathetic nerves and inhibits melatonin synthesis
  2. more hours of sunlight = less melatonin secretion in the spring
  3. decrease in melatonin allows for reactivation of GnRH secretion (in long day breeders)
  4. FSH released first, inducing initiation of follicular growth
  5. mares show estrous behavior and follicular growth but NO OVULATION YET
  6. after 3-4 waves, follicles produce enough estrogen to induce a peak of LH, inducing the first ovulation of the year and the beginning of breeding season!
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8
Q

how long is it from the first follicles to the first ovulation in mares? what does this mean about breeding time?

A

about 60 days, so even though begin getting more light per day after winter solstice, mares not ready to breed until about April, so if breeding in feb or march without success, horse not infertile just not ready

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9
Q

when is the natural horse breeding season? when is the artificial breeding season and why? how is this artificial season induced?

A

natural: april to october/december

artificial: february to june to try to get that january 1st birthday for early foals that are more mature at sales and shows

can induce this early by using artificial lighting beginning around november

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10
Q

why do females have estrous cycles? (2)

A

to increase the chances of becoming pregnant by mating around the time of ovulation and offering repeated opportunities to mate

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11
Q

how long is the equine estrous cycle? what is the day 0 event?

A

21 days; day 0 is ovulation

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12
Q

describe the equine estrous cycle

A

estrus: 5-7 days long
1. FSH high at the beginning of estrus, induces follicular growth; FSH release is favored by tonic GnRH secretion
2. follicles grow on the ovaries and produce estradiol, which induces sexual receptivity
3. increased estradiol triggers the pre-ovulatory GnRH surge, which induces a surge of LH
4. LH surge triggers ovulation (day 0), occurs 1-2 days before the end of estrus

diestrus: 14-16 days long
1. a corpus luteum forms following ovulation
2. the CL produces progesterone, which inhibits sexual receptivity
3. if no embryo is detected, the endometrium releases PGF2alpha on day 14 of the cycle/diestrus)
4. PGF2alpga lyses the CL and terminates diestrus

equines also have transition periods:

between estrus and diestrus: metestrus

between diestrus and estrus: proestrus

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13
Q

do all species ovulate spotaneously?

A

nope! induced ovulators have follicles that will grow like normal but will regress instead of ovulate unless they are bred

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14
Q

what is the purpose of hormonal protocols to control the estrous cycle? (5)

A
  1. estrus synchronization
  2. estrus suppression
  3. estrus induction
  4. contraception
  5. treatment of ovarian pathology
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15
Q

what does administering exoenous progesterone do (1) and why is this done (3)? also give the difference between progesterone and progestagen

A

exogenous progesterone prolongs diestrus for:
1. estrus synchronization
2. estrus suppression/contraception
3. pregnancy maintenance

progesterone and progestagen are DIFFERENT substances! but they act on the same receptors so they have the same effects

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16
Q

what does administering exogenous PGF2alpha do? (1) why is this done? (4)

A

exogenous PGF2alpha lyses the corpus luteum for:
1. estrus synchronization
2. shortening of diestrus
3. treatment of persistent CLs/cysts
4. pregnancy termination

17
Q

what does administering exogenous GnRH do? (1) why is this done? (2)

A

exogenous GnRH induces release of LH for:
1. induction of ovulation
2. treatment of ovarian cysts

18
Q

what does administering exogenous FSH do? (1) and why is this done? 1)

A

exogenous FSH induced follicular growth for superovulation and multiple embryo collection

19
Q

what are the 3 goals of breeding animals efficiently?

A
  1. high pregnancy rate
  2. low cost and labor
  3. large litter size (species dependent)
20
Q

what are the 3 factors to consider when breeding animals?

A
  1. when the female is fertile: relative to time of year and estrous cycle
  2. breeding technique: natural mating or AI
  3. semen quality: fresh, cooled, or frozen semen
21
Q

what are the advantages (5) and disadvantages (5) of pasture mating?

A

advantages:
1. decreased labor
2. decreased animal handling
3. lower personnel cost
4. lower breeding cost
5. decreased interference

disadvantages:
1. decreased genetic improvement
2. increased risk for injury (of animals)
3. male’s favorites; might not breed all females
4. unknown breeding date
5. increased spread of venereal disease

22
Q

compare controlled mating to pasture mating

A

not many advantages, because now requires labor, animal handling, personnel and breeding cost, and interference, while maintaining a higher spread of venereal disease;
genetic improvement is possible if the mates are chosen well but that choice is often limited by location, cost, and female cyclicity

23
Q

give the advantages (5) and disadvantages (5) of AI

A

advantages:
1. increased number of females can be bred
2. increased genetic improvement
3. decreased risk for animal injury
4. decreased risk of venereal disease
5. decreased transportation cost

disadvantages:
1. decreased fertility with freezing semen
2. increased knowledge and skills required
3. increased veterinary cost
4. increased labor and handling
5. increased occupational risk

24
Q

what is the cardinal sign of estrus in ALL species?

A

standing for mating

25
Q

what are 4 secondary signs of estrus in dogs?

A
  1. vulvar swelling
  2. bloody discharge
  3. male attraction
  4. changes in vaginal epithelium: increased thickness and cornification in response to estrogen (which is mitotic and induces cell division); will show 100% cornified cells in canines in full heat
26
Q

what does canine vaginal cytology assess? when is this used (2)?

A

assessment of blood estrogen; used for breeding management and diagnosis of hyperestogenism due to ovaria remnant syndrome or granulosa-theca cell tumors

27
Q

what is ovarian remnant syndrome? (3)

A
  1. recurrent estrus after spaying due to surgeon error failing to remove all ovarian tissue
  2. occurs in 17-43% spayed bitches around 15 months post OHE; remnant tissue must be surgically removed
  3. vaginal cytology is a good way to diagnose (present of cornified cells
28
Q

what are secondary behavioral signs of estrus in mares when teased by stallions? (6)

A
  1. remain calm (don’t try to kill stallion)
  2. raise tail
  3. squat
  4. lean towards stallion
  5. urinating in response to stallion
  6. wink (rhythmic clitoral exposure)
29
Q

other than teasing with a stallion, how can estrus be detected in mares? what will be seen in estrus and in diestrus?

A

transrectal ultrasound

in estrus: will see a fluid filled follicle (an anechoic (black) round structure)

in diestrus: will see a solid corpus luteum (a hyperechoic (gray) round structure)

30
Q

what are behavioral secondary signs of estrus in cattle? (4)

A
  1. restless and walking in search of the bull
  2. bellowing more often
  3. clear, mucoid vulvar discharge; strings of mucus may be smeared on tail or butt
  4. seeking other animals; congregating in small “sexually active” groups that make physical contact with each other (head butting, resting chins on hips, mounting each other)

these signs may start 6-10 hours before estrus and continue throughout estrus; the cow in estrus is the one being mounted!! but closely monitor the other cows in the sexually active group too!

31
Q

how long does estrus usually last in a cow? how does this related to observation frequency for detecting estrus?

A

estrus lasts 15 hours on average, but can range from 6-24 hours, so

observe AT MINIMUM every 12 hours (6am and 6pm), but if observe at 6am, noon, and 6pm, will see a 10% increase in estrus detection, AND if observe at 6am, noon, 6pm, and midnight, will see a 20% increase in estrus detection

32
Q

what are 3 estrus detection aids in cattle?

A
  1. chin marker
  2. heat patch
  3. pedometer

Endocrine/Repro (31 decks)

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