Special Sub-Topic: Mare's Reproductive Cycle Click Here To Play: Mare's Reproductive Cycle

During winter when a mare is not cycling, she is in ___________.

Anoestrus. The mare is stimulated into cycling in spring when daylight hours increase.

The main hormone that makes a mare show she is in season is ________.

Oestrogen/estrogen. Follicles in the ovaries release oestrogen causing the uterus to prepare for a fertilised egg. The mare is then in oestrus/estrus(season) and will be receptive to a stallion.

The period between seasons is called _________.

Dioestrus. Dioestrus lasts an average of 18 days.

A mare is stimulated to begin cycling in spring when the ________ at the base of the brain senses increasing daylight.

Hypothalamus. The hypothalmus senses the increasing daylight. Gonadotrophic releasing hormone then enters the portal system between the hypothalmus and the pituitary gland, causing the front portion of the gland to release follicle stimulating hormone (FSH). FSH causes immature follicles in the mare's ovaries to grow.

When follicles in the mare's ovaries reach at least 2cm, the anterior P_______ gland secretes luteinizing hormone, causing follicles to erupt and release the ovum within.

Pituitary. This is known as ovulation.

Once ruptured, the follicle forms an active corpus luteum and becomes responsible for secretion of __________.

Progesterone. Under the influence of progesterone, the mare will reject a stallion. She is now in dioestrus.

__________ from the ______ ______ keeps the uterine horns in a receptive state so that if sperm fertilises the egg, the embryo will have a suitable home to grow and develop.

Progesterone, Corpus Luteum. This receptive state lasts about 14 days.

After approximately 14 days, if there is no embryo, the uterus will release _________.

Prostaglandin. Prostaglandin will end the corpus luteum and prevent further production of progesterone.

The uterus takes over the production of hormones approximately ___days into pregnancy.

150. If an embryo has been implanted, the corpus luteum will continue production of progesterone and maintain the pregnancy.

The main hormone that makes a mare show she is in dioestrus is _______.

Progesterone. Oestrogen is the main hormone during oestrus. Progesterone is the main hormone during dioestrus, and during anoestrus there is no main hormone because the mare is not cycling.