The developing follicle secretes estrogen which in turn stimulates the follicle to mature rapidly (day 2/3) Estrogen levels increase which triggers LH to mature the follicle and trigger ovulation (day 4/5) Ovulation occurs 24-48 hours before the end of estrus (day 5/6) Increase in estrogen also produces signs of ‘heat’ such as increase in urination, winking and squatting Once ovulation has occurred, FSH & LH are inhibited (by increase in estrogen) so that only 1 secondary oocyte is released
Diestrus
Period of sexual rejection
Lasts 14-15 days
Remnants of the follicle fills with blood to form the corpus lutetium LH stimulates the inner cells to grow rapidly which replaces the blood with a soft yellow cyst like tissue This produces progesterone for the next 14 days, as well as some estrogen, relaxin & inhbin Progesterone acts to prepare and maintain the endometrium for implantation of an embryo and prepare the mammary glands for milk secretion Relaxin relaxes the uterus by inhibiting contractions of the myometrium Inhibin inhibits the secretion of FSH & LH If the mare is not pregnant, progesterone decreases, and a new cycle of estrus begins The corpus luteum is destroyed & reabsorbed by the body If the mare is pregnant, the corpus luteum continues to produce progesterone until the placenta takes over
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