Ovulation in Animals
Ovulation is the process of release of ovum from the follicles in the ovary is called ovulation.
On the surface of the ovary the matured graaffian follicles looks like blisters and continues to swell and finally it ruptures at one point of swelling to release the ova along with the corona radiata cells. The released ova are picked up by the ciliary movements of the fimbriated end of the oviduct and are carried to the site of fertilization.
Commonly there is a seasonal period during which ovulation occurs. The ovulation occurs during estrus in all domestic animals except cow where it occurs 12 hours after the end of estrus.
Types of ovulation
- Spontaneous ovulation: No stimulus is required for ovary. The mating acts as stimulus. Hence the ovulation is independent of mating. E.g. All domestic animals & man.
- Induced ovulation: Stimulus is a must for ovulation. Mating stimulates the release of Leutinizing Hormore (LH) which inturn brings the ovulation. E.g. cat, rat, rabbit and mink.
Type of ovulators
- Based on the side of the ovary which ovulates in mammals are classified as-
- Left ovulators – Swine, Mare and Chicken.
- Right ovulators – Cow and Sheep.
- Both side ovulators – Owl, Hawk and Women.
MECHANISM OF OVULATION
As the follicle matures it bulges from the surface of the ovary. At the apex of the follicle an avascular spot appears and it is called stigma. The follicle ruptures at the stigma and the liquor folliculi is liberated carrying with it the ovum and the discus proligerous.
Theories of ovulation
- Pressure theory: As the follicle matures, the follicular fluid increases in quantity and the pressure brings about the rupture of the follicle. This theory is not accepted in cow, ewe and sow where at the time of ovulation the follicle will be flabby but still ovulation occurs.
- Massage theory: The follicle ruptures by massage action, which lacks proof.
- Hormonal theory: The ovulation takes place by the influence of hormones and is the most accepted theory.