Oestrous Cycle Share
The oestrous cycle of a cow is generally about 21 days long but can span 17-24 days.
The cycle begins with a cow in oestrus.
At this moment the cow reaches its peak oestrogen secretion, which can last from 6 to 24 hours.
Ovulation generally occurs 24 to 32 hours after the beginning of cattle oestrus.
Ovulation marks the beginning of the luteal phase.
After ovulation, germ cells mature in a process called oogenesis.
They are incorporated into follicles that contain receptors for follicle stimulating hormone (FSH). Follicles grow and mature in follicular waves.
Oestrus (day 0 of the cycle) lasts on average 4-24 hours.
- During oestrus, the cow or heifer is receptive to a bull and stands for mating (standing heat).
- Ovulation takes place 30 hours after the onset of oestrus and after behavioural signs have ceased.
- Restlessness
- Decreased milk production
- Standing to be mounted
- Presence of clear mucus
- Swelling and reddening of vulva
Metoestrus (day 2-4) starts when oestrus ends.
- A corpus luteum (CL) from the ovulated follicle is formed.
- Progesterone (P4) levels in circulation begin to rise.
- P4 exerts a negative feedback on the gonadotropin releasing hormone (GnRH) neurons in the hypothalamus limiting the production of cattle oestrogen.
Dioestrus (day 5-17) is the period of maximum CL size and function.
- High levels of progesterone in circulation.
- At the end of dioestrus, luteolysis of the CL begins because of PGF2α produced by the endometrium.
Pro-oestrus (day 17-20) consists of ovarian follicles growing rapidly.
- The CL of the previous cycle regresses.
- Progesterone concentrations in circulation drop.
- The dominant follicle is selected and grows producing increasing amounts of oestradiol.
- Mucosal layers of vagina and uterus multiply.