Changes

* Marked increase in reproductive activity.

* Marked increase in reproductive activity.

* Endocrine transition from progesterone to oestrogen dominance under the influence of gonadotrophins LH and FSH.

* Endocrine transition from progesterone to oestrogen dominance under the influence of gonadotrophins LH and FSH.

* Follicular growth and [[Ovary - Anatomy & Physiology#Corpus_Luteum_Regression|regression of the corpus luteum]] of the previous cycle (in polyoestrous species).

* Follicular growth and [[Corpus_Luteum_Regression|regression of the corpus luteum]] of the previous cycle (in polyoestrous species).

* Uterus enlarges slightly

* Uterus enlarges slightly

* [[Uterus - Anatomy & Physiology#Endometrium|Endometrium]] becomes congested and oedematous, glands show secretory activity.

* [[Uterus - Anatomy & Physiology#Endometrium|Endometrium]] becomes congested and oedematous, glands show secretory activity.

* Longest phase of the oestrous cycle, which usually laste 10-14 days in polyoestrous females.   

* Longest phase of the oestrous cycle, which usually laste 10-14 days in polyoestrous females.   

* The [[The_Ovary_-_Corpus_Luteum_- Anatomy & Physiology|corpus luteum]] is present on the [[Ovary - Anatomy & Physiology|ovary]] and secreting large amounts of progesterone. The duration of this phase is directly related to the time that the [[The_Ovary_-_Corpus_Luteum_- Anatomy & Physiology|corpus luteum]] remains functional.

* The [[Corpus Luteum - Anatomy & Physiology|corpus luteum]] is present on the [[Ovary - Anatomy & Physiology|ovary]] and secreting large amounts of progesterone. The duration of this phase is directly related to the time that the corpus luteum remains functional.

* High progesterone levels prompt the uterus to prepare a suitable environment for development of the embryo, and eventual [[Fertilisation%2C_Implantation_and_Early_Embryonic_Development_-Implantation- Anatomy & Physiology|attachment of the conceptus to the endometrium]] (implantation).

* High progesterone levels prompt the uterus to prepare a suitable environment for development of the embryo, and eventual [[Fertilisation%2C_Implantation_and_Early_Embryonic_Development_-Implantation- Anatomy & Physiology|attachment of the conceptus to the endometrium]] (implantation).

* Uterine glands undergo hyperplasia and hypertrophy.

* Uterine glands undergo hyperplasia and hypertrophy.

* Secretions of the tract are scant and sticky.

* Secretions of the tract are scant and sticky.

* [[Vagina and Vestibule - Anatomy & Physiology#Vagina_2|Vaginal mucosa]] becomes pale.

* [[Vagina and Vestibule - Anatomy & Physiology#Vagina_2|Vaginal mucosa]] becomes pale.

* Ends with the [[Ovary - Anatomy & Physiology#Corpus_Luteum_Regression|regression of the corpus luteum]] (luteolysis).

* Ends with the [[Corpus_Luteum_Regression|regression of the corpus luteum]] (luteolysis).

=== Anoestrus ===

=== Anoestrus ===

* The corpus luteum reaches full size at 4-5 days after ovulation but does not protrude from the ovarian surface.

* The corpus luteum reaches full size at 4-5 days after ovulation but does not protrude from the ovarian surface.

* On section of the ovary, the corpus luteum will appear brown and later yellow.  It is triangular or conical in shape, with the narrow end on the ovulaiton fossa.  The centre of the corpus luteum normally contains dark brown fibrin.

* On section of the ovary, the corpus luteum will appear brown and later yellow.  It is triangular or conical in shape, with the narrow end on the ovulaiton fossa.  The centre of the corpus luteum normally contains dark brown fibrin.

* The corpus luteum of the cycle (non-pregnant) starts to regress on about the 12th day of the cycle.  At the time of [[Ovary - Anatomy & Physiology#Corpus_Luteum_Regression|regression]], there is a fall in blood progesterone concentration.

* The corpus luteum of the cycle (non-pregnant) starts to regress on about the 12th day of the cycle.  At the time of [[Corpus_Luteum_Regression|regression]], there is a fall in blood progesterone concentration.

* As it ages, its colour goes from red to scarlet.

* As it ages, its colour goes from red to scarlet.

* Small remnants can persist for several months.

* Small remnants can persist for several months.

* For more general information on regression of the corpus luteum, click [[Ovary - Anatomy & Physiology#Corpus_Luteum_Regression|here]]

* For more general information on regression of the corpus luteum, click [[Corpus_Luteum_Regression|here]]

==== Size of Ovaries ====

==== Size of Ovaries ====