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Module 22: Reproduction & Fertility > Cow & Ewe Reproduction Basics > Flashcards

Cow & Ewe Reproduction Basics Flashcards

1
Q

how long does the follicular phase last in cows

A

Rising estradiol in follicular phase causes a rise in GnRH which leads to an LH surge causing ovulation

3 days

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2
Q

how long after heat does ovulation occur

A

Ovulation occurs after heat which is 4-12 hours

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3
Q

how long does the luteal phase last

A

17-18d

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4
Q

how many follicular waves do dairy cows normally have

A

2 wave cycles

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5
Q

how many follicular waves do beef cows normally have

A

3 waves

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6
Q

describe the role of the hypothalamus in the estrous cycle of a cow

A

Produces gondadotropin releasing hormone (GnRH):

Positive feedback: estrogen

Negative feedback: progesterone

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7
Q

describe the role of the anterior pituitary in the estrous cycle of a cow

A

Produces follicle stimulating hormone (FSH) and luteinizing hormone (LH) in response to GnRH and estrogen

FSH and LH production is inhibited by progesterone

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8
Q

describe the role of the ovaries in the estrous cycle

A

Follicles produce estrogen

Corpus luteum produces progesterone

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9
Q

describe the role of the uterus in the estrous cycle

A

Produces PGF2a in absence of pregnancy which causes luteolysis

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10
Q

what occurs in the luteal phase

A

Under influence of progesterone

The remnants of the newly ruptured ovarian follicle develop into a corpus luteum and produce progesterone

Progesterone is needed to maintain a potential pregnancy

Over the first 10 days the CL matures and increases in size

Under influence of high levels of progesterone, follicles continue to emerge and regress without a DF

If there is no pregnancy the uterus releasees prostaglandin F2-alpha (PGF2a) which causes the CL to regress (luteolysis)

The low progesterone allows dominant follicle to emerge

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11
Q

how long is the luteal phase in cows

A

17-18d

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12
Q

describe what happens in the follicular phase

A

Under influence of estrogen

There is rapid growth of a dominant follicle and increased estrogen production

Two or three groups of follicles (waves) that develop

Early in the estrous cycle, when P levels are high the dominant follicle in the first wave will not ovulate (becomes atretic)

The high estrogen produced by DF (16-18mm) will cause estrus signs

“standing heat”

Day 0 of cycle

Estrogen triggers the hypothalamus to release a surge of GnRH right before ovulation

GnRH triggers the pituitary to release a surge of LH which causes the DF to rupture approximately 24-32h later and releasing the oocyte

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13
Q

how long is the follicular phase in the estrous cycle

A

3 d

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14
Q

what are the size of dominant follciles in dairy cows

A

9-19mm

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15
Q

describe the annual repro production cycle in dairy cows

A

Dairy cows dried off 6 weeks before they calve

Important for a high milk yield

Cows need to resume normal estrous cycles by 6-7 weeks postpartum to be mated or submitted for AI and achieve pregnancy by 3 months post partum

Essential is timely (by 4-5 weeks) resumption of:

  • Frequent LH pulsatility
  • Dominant follicle growth, E2 secretion
  • DF ovulation
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16
Q

what needs to resume by 4-5 weeks post partum in dairy cows to be pregnant by 3 months post partum

A

Frequent LH pulsatility

Dominant follicle growth, E2 secretion

DF ovulation

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17
Q

what factors reduce GnRH and LH pulse frequency and prolonging the interval to 1st ovulation in dairy cows

A

BCS at calving

Negative energy balance pp —> loss of >0.5 BCS

LH pulsatility will be compromised and first dominant follicle will not ovulate causing a longer interval to first ovulation

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18
Q

what factors reduce GnRH and LH pulse frequency and prolonging the interval to 1st ovulation in beef cows

A

Low BCS at calving:

  • If cow is too thin during late gestation period, then they calve down at low BCS which will reduce the LH pulsation frequency and prolong the interval to return to cycling post partum

Nutrition

Suckling

Maternal bond

  • Presence of the calf
  • Breed dependent
  • Continental breeds more susceptible
19
Q

what is the biggest challenge getting dairy cows to resume cyclicity

A

Negative energy balance period

  • Need to have cyclicality at 6-7 weeks so she will get pregnant by 3 months post partum
20
Q

what are negative effects on ovarian function and the hypothalamic-pituitary axis

A

Metabolic state can negatively influence GnRH and LH pulsatility

There are also negative effects on the metabolic state as well such as lactation, genetics, nutrition

At onset and during lactation disease also influences ovarian function:

  • Uterine infection
  • Mastitis post partum
21
Q

why is heat detection difficult

A

labour intensive

3-5x daily

can be impractical

22
Q

what are common heat detection aids

A

Synchronization of heat or ovulation

Tail painting

Kamar heat detector

Vaginal resistance (drop with LH surge)

Pedometers/activity monitors and software

23
Q

what is the most important factor in successful fertilization and development of a good quality embryo

A

timing the AI correctly

24
Q

what happens if AI is done too early

A

low fertilzation rate

with a high quality embryo

By the time ovulation occurs which could be a day later the sperm will be dying off

25
Q

what happens if the AM/PM rule is done

A

good fertilization rate and good quality embryo

a compromise

Animal that comes into heat in the morning will be inseminated in the evening

Always aiming to inseminate animals about 12 hours after the onset of heat

Achieve the highest conception rates

26
Q

what happens if AI is done too late

A

high fertilzation rate and low embryo quality

By the time sperm has capacitated the egg will decline and become atretic

Less sperm selection and/or aging ovum

27
Q

when can heatcheck be used to pregnancy diagnose

A

18-24d

28
Q

when can a CL check be used to pregnancy diagnose

A

18-24d

29
Q

when can elevated milk/plasma progesterone be used to pregnancy diagnose

A

22-26d

30
Q

when can a transrectal ultrasound be used to diagnose pregnancy

A

25 + days

31
Q

when can palpation of the amniotic vesicles be used to diagnose pregnancy

A

42+ days

32
Q

when can palpation of the placentomes and fluids be used to diagnose pregnancy

A

2.5 months

33
Q

when can the fremitus of pregnant horn be felt

A

3.5+ months

34
Q

when can an estrone sulphate assay be used to diagnose pregnancy

A

105+ days

35
Q

when can fremitus of non pregnant horn be palpated

A

150+ days

36
Q

what occurs during early pregnancy

A

The embryo enters the uterine horn approximately day 4

At day 8 the blastocyst hatches from the zona pellucida and expands

At day 12-14 the expanding blastocyst produces trophoblast protein which induces maternal recognition of pregnancy which means there will be maintenance levels of progesterone

CL function maintained and P continues to rise and support the embryo for quite a long time

37
Q

in order for a successful pregnancy to occur what must happen and how does this happen

A

Pregnancy in ruminants only successful if maternal recognition of pregnancy = CL maintenance

  • Bovine trophoblast protein is secreted from the expanding blastocyst just before the time of normal regression of CL
  • It suppresses PGF2alpha and no luteolysis so CL maintained and produces P to support the pregnancy
38
Q

how long is the estrous cycle in ewes

A

17d

39
Q

how long is the luteal phase in ewes

A

14d

40
Q

how many follicle waves do ewes have

A

2-4 waves per cycle

41
Q

when does ovulation occur in the ewe

A

Ovulation at end of estrus (24-36 hours)

  • Longer time period than cattle
  • Ovulation occurs at the end of estrus —> in cows ovulation occurs after estrus is finished
42
Q

how do multiple ovulations occur in the ewe

A

Multiple ovulations derive from last two waves (co-dominance, DFs from second last and last wave)

43
Q

what type of breeders are ewes

A

Seasonal (short-day breeders)

The changes in the photoperiod = day length synchronizes their reproductive cycles via melatonin with the pineal gland

44
Q

how can you advance the breeding season in ewes

A

In summer melatonin production is low because there is less darkness

In winter long production of melatonin

Decline in day length must occur for the breeding season to begin (autumn)

Exogenous melatonin 2x 30d

  • Works by overriding the inhibitory effects of long summer days, after the ewes have seen the increase in day length in spring
  • Early breeding season advanced by 2 months

Module 22: Reproduction & Fertility (27 decks)

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