Bovine Reproduction Flashcards
When can cyclicity of oestrus cease?
- Pregnancy
- Nursing
- Season- some species
- Nutrition
- Stress
- Pathologic conditions
What are the different types of oestrus cycles?
- Polyoestrus- constant- cows, cats, rodents
- Seasonal polyoestrus- mare/sheep- long/short days
- Monoestrus- dogs
How can the oestrus cycle be divided into 2 distinct phases?
Follicular Phase:
* period from the regression of corpora lutea to ovulation
* Primary ovarian structures are growing dominant follicles that produce oestradiol
Luteal Phase
* Period from ovulation until corpus luteum regression
* Dominant ovarian structures are the corpus luteum
* Primary repro hormone is progesterone
* follicles continue to grow and regress but do not produce high amounts of estradiol
What is the difference between oestrogen and oestradiol?
- Oestrogen is a type of sex hormone which has 3 types
- Oestrone (E1)
- Oestradiol (E2)
- Oestriol (E3)
When does the follicular phase commence and what does it cause?
- After luteolysis
- Causes a decline in progesterone
- Gonadotrophins (FSH and LH) are therefore produced that causes follicles to produce oestrogen
What hormone dominates the follicular phase?
When does the follicular phase end?
- E2 (oestradiol)
- Follicular phase ends at ovulation where the luteal phase commences
When does the luteal phase start?
What does it include?
What causes luteolysis to end the luteal phase?
- After ovulation
- Includes the development of the corpus luteum
- prostaglandin F2alpha causes luteolysis
How can the oestrus cycle be divided into four stages?
Follicular phase: proestrus and oestrus
Luteal phase: Metoestus and Diestrus
- When does proestrus begin?
- What ‘characterises’ proestrus?
- What happens during proestrus?
- Luteolysis- progesterone declines
- Endocrine transition- progesterone to oestrogen dominance
- Follicles recruited for ovulation and female repro system prepares for oestrus
- What is the dominant hormone durine oestrus?
- What is standing oestrus?
- Oestrodiol
- Willingness to accept the male for mating
What occurs during metoestrus?
- During early metoestrus progesterone and oestrogen are low
- The newly ovulated follicle undergoes cellular and structural remodelling forming the corpus luteum
- This process is called lutenization
- Progesterone secretion is detectable soon after ovulation
- But 2-5 days before corpus luteum produced significant quantities
What occurs during dioestrus?
- CL fully functional
- Progesterone secretion high
- Ends with luteolysis
- High progesterone prompts the uterus to prepare a suitable environment
What is silent ovulation?
- Following seasonal anoestrus in the ewe or pregnancy in a cow
- Ovary develops a follicle that ovulates without behavioural oestrus
- The CL produced primes the brain enabling E2 for the next ovulatory follicle
What is lactational anoestrus?
- Cyclicity is delayed by a nursing neonate
- Causes inhibition of GnRH
What ‘governs’ the follicular phase?
- The hypothalamus and anterior lobe of the pituitary and ovary control the production of oestrodiol in the absence of progesterone
What does the hypothalamus release for the oestrus cycle?
GnRH
What are the two different centres of the hypothalamus that control GnRH release?
Tonic GnRH centre:
* responsible for basal secretion of GnRH
Surge centre:
* responsible for the preovulatory causing LH surge
* Releases basal until positive stimulus
* Positive stimulus is high oestrogen with low progesterone
Describe the release and control of FSH and LH during the follicular phase
- GnRH pulse frequency increases due to low progesterone
- FSH and LH secreted from anterior lobe
- Oestrodiol released from follicles
- The gonadotrophins have postitive feedback causing GnRH release
- Follicle releases oestrodiol and later on inhibin which causes negative feedback on FSH
Describe the hormonal changes during oestrus
- Recruited follicles develop dominance
- Produce oestrodiol and inhibin
- Supress FSH- does not surge like LH
- When oestrogen reaches a threshold peak preovulatory surge of LH occurs
What do the dynamics of antral follicles consist of?
- Recruitment
- Selection
- Dominance
- Atresia
Describe the process of recruitment, selection and dominance of follicles
Recruitment
* Small antral follicles are recruited from ovarian pools
* Produce small amounts of E2
* Some atresia
Selection:
* Follicles are selected from pre-viously recruited small follicles
* Develop further- moderate E2
* Some become atretic
Dominance:
* Selected follicles that do not become atretic become dominant and produce large amounts of E2
* Dominant follicles will ovulate
Why during the first two follicular waves does full development and ovulation not occur?
- Begin and terminate during times in the cycle when progesterone is increasing or at highest point
- Dominant follicle will ovulate if luteolysis occurs
Are the FSH, LH and inhibin high or low during:
1. Recruitment
2. Selection
3. Dominance
- Recruitment- high FSH, low LH, no inhibin
- Selection- low FSH, moderate LH, low inhibin
- Dominance- low FSH, high LH, high inhibin
What do each of the images show?
Top:
* Ovary containing small antral follicles (SF)
Middle:
* Ovary contains three medium antral follicles MF
* An a corpus luteum
Bottom:
* Contains a dominant follicle
* OS- ovarian stroma
