Reproduction - Comparative Oestrus Cycles & Pharma Flashcards Preview

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Flashcards in Reproduction - Comparative Oestrus Cycles & Pharma Deck (49)
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1

What is the total length of oestrus (ovulation to ovulation) for the mare?

21 days

2

How long is oestrus in the mare (standing behaviour as Day 1)?

4-8 days

3

What is the length of the oestrus cycle in the sow?

21 days

4

What is the length of oestrus in the ewe?

17 days 

Every 17 days in the fall & winter, te ewe will ovulate (if she isn't impregnated right away).

5

What is the length of oestrus in the bitch?

93 days. 

 

6

What is the length of oestrus in the queen?

It's variable.

7

What is the length of the oestrus cycle in the woman?

28 days.

However, women don't mark their ovarian cycles by the start of oestrus, but by the appearance of menses, and thus they mark the menstrual cycle rather than the oestrus cycle. Ovulation occurs in the MIDDLE of the woman's menstrual cycle, whereas ovulation typically occurs a few days after the start of the oestrus cycle in domestic animals.

8

In domestic animals, is the follicular phase of the oestrus cycle longer or shorter than the luteal phase? 

How does this compare with the two phases in the woman?

In domestic animals, the follicular phase is much shorter than the luteal phase. 

In humans, the follicular & luteal phases are the same length (14 days & 14 days).

9

How long does oestrus last during the oestrus cycle (ie., when the animal is receptive) in the mare?

4-8 days

10

How long does oestrus last during the oestrus cycle (ie., when the animal is receptive) in the cow?

4-24 hours

(also cited as 12-36 hours)

In cow, oestrus tends to be nocturnal; oestrus must be observed, marked by standing when mounted, Flehmen, lordosis, swollen vulva, etc.

11

How long does oestrus last during the oestrus cycle (ie., when the animal is receptive) in the ewe?

24-48 hours

The ram has to be fast!

12

How long does oestrus last during the oestrus cycle (ie., when the animal is receptive) in the sow?

48-96 hours 

(2-4 days)

13

How long does oestrus last during the oestrus cycle (ie., when the animal is receptive) in the bitch?

7-13 days

Note that the bitch only ovulates one every 93 days, so if she doesn't become pregnant during the 7-13 days she's in heat, then she has a very long period -- almost three months -- before she will ovulate again. In reality, the bitch goes through a very long period of anoestrus when she won't come into heat at all, so she might come into heat less than once a year.

14

How long does oestrus (heat) last during the oestrus cycle in the queen?

4-10 days. This is when you hear queens yowling. 

15

How long does oestrus (heat) last in women?

There is no "oestrus period" in the same way domestic animals go into heat.

16

The follicular phase of the oestrus cycle is when oestrogen is dominant; it is rising as the dominant follicles prepare to ovulate and the granulosa cells continue to convert testosterone from the theca cells, using aromatase, into oestrogen.

When the oestrogen plasma concentration reaches a threshold, oestrogen will switch from providing negative feedback to the hypothalamus for GnRH production and the anterior pituitary for LH secretion to positive feedback

In the mare, how long is this follicular stage?

 

Variable, but about 7 days. 

17

The follicular phase of the oestrus cycle is when oestrogen is dominant; it is rising as the dominant follicles prepare to ovulate and the granulosa cells continue to convert testosterone from the theca cells, using aromatase, into oestrogen.

When the oestrogen plasma concentration reaches a threshold, oestrogen will switch from providing negative feedback to the hypothalamus for GnRH production and the anterior pituitary for LH secretion to positive feedback.

In the cow, how long is this follicular stage?

 

4 days

18

The follicular phase of the oestrus cycle is when oestrogen is dominant; it is rising as the dominant follicles prepare to ovulate and the granulosa cells continue to convert testosterone from the theca cells, using aromatase, into oestrogen.
When the oestrogen plasma concentration reaches a threshold, oestrogen will switch from providing negative feedback to the hypothalamus for GnRH production and the anterior pituitary for LH secretion to positive feedback.

In the ewe, how long is this follicular stage?
 

Three days

19

The follicular phase of the oestrus cycle is when oestrogen is dominant; it is rising as the dominant follicles prepare to ovulate and the granulosa cells continue to convert testosterone from the theca cells, using aromatase, into oestrogen.
When the oestrogen plasma concentration reaches a threshold, oestrogen will switch from providing negative feedback to the hypothalamus for GnRH production and the anterior pituitary for LH secretion to positive feedback.

In the sow, how long is this follicular stage?
 

Seven days

20

The follicular phase of the oestrus cycle is when oestrogen is dominant; it is rising as the dominant follicles prepare to ovulate and the granulosa cells continue to convert testosterone from the theca cells, using aromatase, into oestrogen.
When the oestrogen plasma concentration reaches a threshold, oestrogen will switch from providing negative feedback to the hypothalamus for GnRH production and the anterior pituitary for LH secretion to positive feedback.

In the bitch, how long is this follicular stage?
 

18 days

21

The follicular phase of the oestrus cycle is when oestrogen is dominant; it is rising as the dominant follicles prepare to ovulate and the granulosa cells continue to convert testosterone from the theca cells, using aromatase, into oestrogen.
When the oestrogen plasma concentration reaches a threshold, oestrogen will switch from providing negative feedback to the hypothalamus for GnRH production and the anterior pituitary for LH secretion to positive feedback.

In the queen, how long is this follicular stage?
 

Variable

NB the luteal phase is 40 days, and the entire oestrus cycle is variable, so it's definitely less than 40 days! Probably a few days.

22

The follicular phase of the oestrus cycle is when oestrogen is dominant; it is rising as the dominant follicles prepare to ovulate and the granulosa cells continue to convert testosterone from the theca cells, using aromatase, into oestrogen.
When the oestrogen plasma concentration reaches a threshold, oestrogen will switch from providing negative feedback to the hypothalamus for GnRH production and the anterior pituitary for LH secretion to positive feedback.

 

In the woman, how long is this follicular stage?
 

14 days. Same as the luteal phase.

23

Physiological interventions can be used to achieve cyclical synchronisation in a herd or to induce ovulation (can be for an individual animal or in a herd). The ways these physiological interventions work are not all completely known, but in general, they stimulate or inhibit endogenous reproductive hormones via the hypothalamus-pituitary-gonadal axis.

Give an example of a physiological intervention used to achieve cyclical synchronisation in a herd of ewes.

State how it works, as well as the advantages & disadvantages.

Ram effect. 

- remove rams from ewes during anoestrus up to six weeks before expected oestrus

- isolate rams for 3-4 weeks, then re-introduce to ewes

- majority ewes ovulate w/i 6 days

- priming & then removal of progesterone (sponges, IM
injections) pre-intro ↑ ewes in oestrus - priming extends the luteal phase, then removing the sponge at the same time -- sudden reduction in progesterone, like luteolysis -- causes them to start ovulating together

Advantages: cheap, can affect whole herd
Disadvantages: only works @ certain times of year (ie., just before start of natural breeding season); doesn’t work in deep anoestrus (eg., July)

24

What type of physiological intervention can be used to induce ovulation in ewes?

Ram effect. Same idea as in achieving synchronization in a herd.

25

Physiological interventions can be used to achieve cyclical synchronisation in a herd or to induce ovulation (can be for an individual animal or in a herd). The ways these physiological interventions work are not all completely known, but in general, they stimulate or inhibit endogenous reproductive hormones via the hypothalamus-pituitary-gonadal axis.

Give an example of a physiological intervention used to achieve cyclical synchronisation in a herd of cows.

State how it works, as well as the advantages & disadvantages.

Can use a teaser bull, but oestrus (heat) is very short, ranging from 12-36 hours, and is highly variable among individual cows.

Physiological intervention is not as successful in synchronising cows, as they are not seasonal breeders and thus their oestrus isn't as predictable or detectable. Their cycles are slightly longer than ewes at 21-24 days, and they typically display oestrus at night (so difficult to detect). 

26

What are pharmacological interventions that can be used to achieve synchronisation in a herd of ewes?

1. Progesterone (P4) - eg. sponge

2. Prostaglandin F2-alpha (PGF2a) - injection

3. Melatonin

27

How is progesterone used to synchronize a herd of ewes? What are the advantages & disadvantages?

Basically: introduction of P4 via sponge extends/coincides with luteal period -- gets all the sheep on same luteal phase --  then sudden removal "tricks" them into thinking luteolysis has occurred as P4 levels suddenly drop off. Then, FSH & LH rises & follicular phase can begin. 

Specifically:  

- in cyclic ewes, P4 suppresses pre-ovulatory release of LH/FSH → inhibits follicular growth & ovulation

- upon removal of progestagen, (-) feedback removed → gonadotrophins ↑ → E2↑→ oestrus → ovulation

- in anoestrus ewes, P4 withdrawal is complemented by follicle-stimulating treatments eg. PMSG (pregnant mare’s serum gonadotrophin)


- Sponges, implants via intravaginal, IM, SC; intravaginal sponges most common, provide good results after natural mating

- sponges contain: synthetic progestagens, fluorogestone acetate (FGA) or medroxy progesterone acetate (MAP)

Advantages: can even work in June, when ewes are in deep anoestrus

Disadvantages: progestagen treatment must last for length of luteal phase, ie., 12-14 days, so sponge must stay in; labour-intensive

28

How are prostaglandins used to synchronise a herd of ewes? What are the advantages and disadvantages?

 PGF2α & analogues synchronize oestrus in cyclic ewes:

- induce luteal regression → P4 ↓ → (-) feedback removed → LH/FSH ↑ → ↑ follicular growth → E2 ↑ → oestrus w/i 2-3 days → ovulation

Disadvantages:
- CL only responsive between days 5-14 of cycle (otherwise refractory), so would need two injections 10-14 days apart

- imprecise & labour intensive; not very
successful, really

- induced oestrus leads to poor fertility, poss. due to limited exposure of tract to P4 (progesterone prepares increases uterine milk & reduces uterine motility in preparation for implantation)

29

How is melatonin used to synchronise oestrus in a herd of ewes? What are the advantages & disadvantages?

- ↑ darkness = ↑ melatonin secreted by inhibited pineal gland (ewes come into oestrus as days shorten; when pineal gland is inhibited due to less neural excitation from daylight, it secretes MORE melatonin)

An increase in melatonin stimulates GnRH from the hypothalamus, triggering LH & FSH production ie., oestrus cyclicity

- used to advance onset of oestrus in seasonally anoestrus ewes


Disadvantages:
- treatment must be initiated after period of LONG day-length (ie., summer), then elevate melatonin for ~5 weeks; maybe easier to herd ewes in a barn & regulate lighting.

30

What are non-physiological methods of inducing ovulation in ewes?

1. Nutrition - flushing with Lupin grains (might increase leptin in adipose tissue)

2. Genetics - "F" (fecund") gene, aka Boorola in Merino breed

3. Gonadotrophins

4. Immunisation / Vaccines

 

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