Overview
The cow's ovaries (ovaria) are oval, flattened and almond-shaped, small relative to the size of the animal. They are suspended by the mesovarium, part of the broad ligament, and lie on either side of the pelvic inlet, next to the tips of the horns. In multiparous cows the heavier uterus pulls them cranially and ventrally into the abdomen. The ovarian bursa, formed by the mesosalpinx, is wide and open, and the oviduct runs along its edge.
Structure and cycle
- Follicles: develop in waves, several per cycle; the dominant follicle of the last wave ovulates. Follicles bulge from the surface and feel like soft, fluctuant areas.
- Corpus luteum (corpus luteum): forms after ovulation, often protrudes from the surface with a crown and is firm. It secretes progesterone and maintains pregnancy.
- Oestrous cycle: lasts about three weeks; if there is no pregnancy, prostaglandin F2α from the uterus destroys the corpus luteum.
Clinical relevance
- Rectal palpation and ultrasound: identify follicles and the corpus luteum, establish the stage of the cycle and diagnose anoestrus or ovarian disorders.
- Cystic ovarian disease: anovulatory structures larger than a preovulatory follicle that persist in the absence of a corpus luteum. Thin-walled follicular cysts and thick-walled luteal cysts are most common in high-yielding dairy cows after calving and cause anoestrus or irregular heats.
- Oestrus synchronisation: protocols with GnRH and prostaglandin F2α act on the follicles and the corpus luteum.
- Manual enucleation of the corpus luteum: discouraged because of the risk of haemorrhage and adhesions.
- Freemartinism: in the female twin of a male the gonads are hypoplastic.