Induced ovulation (animals)

Ovulation occurs at the ovary surface and is described as the process in which an oocyte (female germ cell) is released from the follicle.

However the monthly menstruation process is typically linked to humans and primates,[4] all other animal species ovulate by various other mechanisms.

Spontaneous ovulation is the ovulatory process in which the maturing ovarian follicles secrete ovarian steroids to generate pulsatile GnRH (the neuropeptide which controls all vertebrate reproductive function) release into the median eminence (the area which connects the hypothalamus to the anterior pituitary gland) to ultimately cause a pre-ovulatory LH surge.

Usually, spontaneous steroid-induced LH surges are not observed in induced ovulator species throughout their reproductive cycles, which indicates that GnRH release is absent or reduced due to lack of positive feedback action from steroid hormones.

Animals that have large, complex social groups benefit from spontaneous ovulation as only the best males get to breed with females.

If there are few males suitable for breeding it makes sense to spread out the times at which females are fertile, therefore increasing the proportion in which conception occurs.

In spontaneous ovulators, estrogen and progesterone secreted by the follicles as they grow and mature affects the release of GnRH, and therefore causes an LH surge.

The pathways in which information reaches the brain and causes GnRH release are not understood well; however, midbrain and brainstem noradrenergic neurones appear to be activated in response to intromission during mating.

However, one possible reason is that induced ovulation could provide a better reproductive potential for those species that typically have shorter life spans and less encounters resulting in lower mating opportunities throughout their lifetime.

The East African mole rat has been found to have small spines on its penis which are also thought to contribute to this stimulation of induced ovulation.

The koalas require mating in which the presence of ejaculated semen is needed to stimulate the female to produce a LH surge (which would cause ovulation of a follicle).

After mating, the LH levels in female cats surge, and the time to ovulation can be predicted to occur between 1–2 days later.

[19] In Japanese black bears, the presence of a male was enough to cause a notable rise in progesterone levels even without mating.

In China freshwater fish including a variety of carp types, bream and loach are able to be induced to ovulate by using agonists of dopamine.

[22] Induced ovulation can be utilized during the warmer seasons to increase plasma progesterone and improve the fertility of the cattle.