Bovine Therio - 1 Estrous Cycle and Reproductive Endocrinology

Question 1

Bovine are what kind of breeders

Answer 1

Non seasonal polycyclic

Question 2

Bovine female reaches puberty at what age

Answer 2

7-18mths (avg. 10mths)

Question 3

The bovine oestrous cycle length is

Answer 3

18-24days (avg. 21days)

Question 4

The bovine oestrus cycle is divided into two phases, name and define them

Answer 4

Luteal phase: 14-18days the period following ovulation when the corpus luteum is formed (met-estrus and diestrus)
Follicular phase: 4-6days the period following the demise of the CL until ovulation (pro-estrus and oestrus)

Question 5

Bovine oestrous cycle is divided into how much follicular waves and how long does each wave take

Answer 5

2-3 follicular waves

7-10days appart

Question 6

During bovine oestrous cycle, what happens to the ovulatory follicle during the follicular phase

Answer 6

Maturation and ovulation, the oocyte is released into the oviduct allowing the potential for fertilization

Question 7

The bovine oestrous cycle is regulated by hormones from various locations, name them and their location

Answer 7

Gonadotrophin-releasing hormone (GnRH) - Hypothalamus
Follicle-stimulating hormone (FSH) & Luteinizing hormones (LH) - Anterior pituitary
Progesterone (P4), Estradiol (E2) & Inhibin - Ovaries
Prostaglandin F2α (PGF) -Uterus

Question 8

Describe Bovine Luteal phase Metoestrus

• Day
• CL?
• Uterine tone
• Other?

Answer 8

Day 1-4
Ovulation depression > Corpus haemorrhagicum > Early CL
Within 48hrs - CL 1.4cm
Uterus - slight tone/oedema/flaccid
Metoestral bleeding (only occurs in cattle
Ova Transport time 3-4 days

Question 9

Describe Bovine Luteal phase Diestrus

• Day
• Dominant hormone
• CL
• Uterine tone
• Cervix

Answer 9

Day 6-18
Progesterone
Palpable papilla (CL)
Flaccid uterus
Cervix closed

Question 10

In non pregnancy, describe the continuation of follicular development (pro-oestrus)

Answer 10

PGF secreted by the endometrium > regression of the CL > fall in progesterone > BPO axis > GnRH > FSH > Follicular development

Question 11

Describe Bovine Follicular phase Pro-oestrus

• Day
• Dominant hormone
• CL
• Follicle
• Uterine tone
• Vulva
• Signs

Answer 11

Day 19-20
FSH
CL 1.5-2cm
F 1.5-2cm
Moderate uterine tone
Vulva swollen
Signs: slight mucous, mounting behaviour

Question 12

Describe Bovine Follicular phase Oestrus (prior to ovulation)

• Day
• Dominant hormone
• CL
• Follicle
• Uterine tone
• Cervix
• Vagina
• Vulva
• Signs

Answer 12

Day 21
Oestrogens (esp. Estradial) & baseline progesterone (due to regression of CL)
CL 1.5cm
Rapidly growing dominant F
Marked uterine tone
Dilated cervix
Vagina mm pink
Vulval oedema
Signs: thick mucous discharge, oestrus behaviour

Question 13

What is the duration of bovine oestrus (not oestrous cycle)

Answer 13

8-12hrs

Question 14

When does ovulation occur in the bovine

Answer 14

After END of oestrus

Question 15

When is the best time (best fertility) to AI a bovine

Answer 15

Mid-oestrus to few hrs after end of oestrus

Question 16

Ovulation in the bovine, is the beginning of the oestrus cycle (day 0). Define it.

Answer 16

The rupturing of the follicle that releases the ovum

Question 17

The same hormones that control the timing of ovulation in the bovine, control what else

Answer 17

Behavioural estrus (heat)

Question 18

Both timing of ovulation and estrus is controlled by the same hormones in the bovine. What hormone is this? Where does it act and why is this important

Answer 18

Estradiol on the hypothalamus, uterus and higher brain (behavioural change). Easier to detect optimum fertility

Question 19

After ovulation in the bovine, the ruptured follicle becomes what?

Answer 19

Corpus luteum

Question 20

The bovine CL is formed under the influence of what

Answer 20

Pituitary LH

Question 21

The bovine CL decides the length of the oestrus cycle?

Answer 21

Yes

Question 22

What is the function of the bovine CL

Answer 22

Secretion of progesterone

Question 23

The bovine CL is responsive to PGF after how many days

Answer 23

5/6

receptors acquired

Question 24

What day does the bovine CL reach max size

Answer 24

7-8th CL 2-2.5cm

Question 25

What is the purpose of the progesterone produced by the bovine CL

Answer 25

To establish and maintain pregnancy

Question 26

If bovine pregnancy does not result, another hormone is released which lyse the CL. What is the hormone and where does it come from? And when does it occur

Answer 26

Prostaglandin F2α from uterus at day 17/18

Question 27

What happens when the bovine CL degenerates

Answer 27

Decline in progesterone

Question 28

Following the decline the progesterone in the bovine estrous cycle there is a rise in another. What hormone is this

Answer 28

Increase in Oestrogen (mainly oestradiol-7)

Question 29

When does the peak in Oestrogen during the bovine oestrous cycle occur

Answer 29

Right before onset of oestrus

Question 30

What effect does oestrogen have on the hypothalamus during the bovine oestrous cycle

Answer 30

Stimulates the release of GnRH

Question 31

What is the effect of preovulatory GnRH in the bovine

Answer 31

Stimulates the release of FSH and LH

Question 32

What is the function of FSH in the bovine oestrous cycle

Answer 32

It stimulates a group of follicles to grow (recruitment)

Question 33

What is the function of LH in the bovine oestrous cycle

Answer 33

After recruitment of a group of follicles, LH is responsible for keeping them growing

Question 34

What happens when there is a dominant ovarian follicle in the bovine

Answer 34

It produces estradiol and inhibin

Question 35

What are the functions of estradiol and inhibin secreted by the DF in the ovary in bovines

Answer 35

It prevents the growth of other follicles

Question 36

Estradiol and Inhibin also affect the hypothalamus in what way in the bovine oestrous cycle

Answer 36

Inhibin: decrease FSH
Estradiol: Preovalatory LH surge

note progesterone level must be low i.e after CL regression

Question 37

Remember, there are 2 to 3 follicular waves in the bovine. Which means there is recruitment of follicles several times. Why does this occur?

Answer 37

Because the CL is still present with progesterone and will not allow maturation of the follicle

Question 38

At the last follicular wave during the bovine oestrous cycle, the last bit of estradiol is “squeezed” out by

Answer 38

Oxytocin

Question 39

LH other than stimulating bovine follicle growth is also stimulates…..

Answer 39

Ovulation