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Oestrous Cycle - Anatomy & Physiology (view source)
Revision as of 12:06, 10 September 2008
, 12:06, 10 September 2008→Oestrous Cycle
=== Oestrous Cycle ===
=== Oestrous Cycle ===
* Seasonal breeder (long day)
* Oestrous cyclicity from spring-autumn. During the winter, the mare is normally anoestrus.
* Winter anoestrus is follwed by a transition to regular cyclic activity. During this time, the duration of oestrus may be irregular or very long.
* Before the first ovulation, behavioural oestrus may not be accompanied by the presence of palpable follicles on the ovary.
* Some long oestrus periods in spring are anovulatory.
* Average cycle length is 20-23 days. The cycles are longest in spring and shortest from June-September.
* Oestrus lasts 6 days.
* Dioestrus lasts 15 days.
* Ovulation occurs on the penultimate day or last day of oestrus.
* The diameter of a ripe follicle ready to ovulate is 3-7cm. The day before ovulation, the tension in the follicle is reduced. Palpation of a large, fluctuating follicle is a reliable sign of impending ovulation.
* The onset of oestrus after foaling is known as the 'foal heat'.
* Occurs on day 5-10 post-parturition.
* Sometimes shorter than normal, lasting 2-4 days.
* The first two post-parturient cycles are a few days longer than normal.
* During Oestrus, a single egg is usually released. Thus, the mare is monotocious.
* Ovulation seems to occur more frequently from the left ovary.
* All ovulations occur from the ovulation fossa.
* Due to the reversed structure of the ovary, corpora lutea may only be seen sometimes at the ovarian hilus. However, because the ovary is curved and mostly covered by fimbrae of the oviduct, corpora lutea cannot be identified by rectal palpation.
* Only fertilized eggs can pass into the uterus.
* Non-fertilized eggs remain in the Utero-Tubal junction for months, where they finally disintegrate.
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=== Endocrine Changes During the Oestrous Cycle ===
=== Endocrine Changes During the Oestrous Cycle ===