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* Immediately after ovulation, the ruptured follicle is seen as a congested depression on the ovary.
 
* Immediately after ovulation, the ruptured follicle is seen as a congested depression on the ovary.
 
* Accumulation of blood clot soon gives the ruptured follicle a conical shape.
 
* Accumulation of blood clot soon gives the ruptured follicle a conical shape.
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* By day 3 after ovulation, its cavity is filled with a dark red blood clot.
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* By day 6, the blood clot is replaced by a connective tissue plug, or slightly yellow fliud.
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** Clots may persist up to day 12.
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** Fluid may persist up to day 18.
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* Corpora lutea attain maximum size at 12-15 days post-ovulation.
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* After this, they gradually regress to the next oestrus.
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* They are dark red up to day 3.
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* They then change colour and remain 'wine red' up to day 15.
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* As the corpus luteum regresses between days 15-18, the colour rapidly changes to yellow, creamy yellow or buff.
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* The mechanism of luteolysis is not fully understood in the sow.
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** Corpora lutea are unresponsive to PGF2
    
=== Endocrine Changes during the Oestrous Cycle ===
 
=== Endocrine Changes during the Oestrous Cycle ===
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