Oestrus cycle
repetitive patterns of hormones and behaviour which lead to the ovulation of a follicle (oocyte release).
Can be describe in terms of hormones, state of the ovaries and behaviour.
How long is the oestrus cycle in the cow?
21 days
(18-24 days)
What are the phases of the oestrus cycle (classified behaviourally)?
- Prooestrous
- Oestrus
- Metoestrus
- Dioestrus
What are the phases of the oestrus cycle (classified by ovarian activity)?
- Follicular phase - oestradiol dominates
- Comprises pro-oestrus and oestrus phase
- Luteal phase - progesterone dominates
- Comprises metoestrus and dioestrus
How does the luteal phase end?
- Absence of foetus –> leads to luteolysis
- Progesterone falls as a consequence of luteolysis
- Progesterone falling enables oestradiol and therefore LH to rise.
- Positive feedback eventually results in LH surge which triggers ovulation during oestrus (follicular phase)
Dominant follicle
Fluid filled structure containing a single egg
Dominant over other follicles on the ovary
Forms corpus luteum once ovulated
There can be multiple dominant follicles
Metoestrus
Succeeds oestrus and sees the formation of the corpus luteum
Describe the hormonal and behavioural indications of oestrus
- High E2
- Female is receptive to the male
- Signs differ between species, include:
- Lordosis
- Lifting tail
- Swollen vulva
- Restlessness/seeking male
- Standing to be mounted
Describe the hormonal and behavioural indicators of dioestrus
- High levels of P4
- Female rejects the male
- May be openly aggressive
When is d0 or d1?
1st day of cycle
= 1st day of oestrus
This is different to the menstrual cycle (where ovulation is mid-cycle as opposed to near the start)
Describe the hormonal, physiological and behavioural changes in the follicular phase
Follicular phase = pro-oestrus + oestrus
- The ovarian follicles mature, secreting increasing concs. of E2 into the blood
- LH rises to surge at ovulation
- FSH rises then falls at the end of oestrus
- Oestrus behaviour is observed
Describe the hormonal, physiological and behavioural changes in the luteal phase
Luteal phase = metoestrus + dioestrus
- Ovarian follicle(s) ovuluate to produce 1+ corpus luteum
- CL secretes progesterone into the blood
- This phase ends with luteolysis caused by PGF2a
- Follicles continue to develop in waves but fail to ovulate
