* Progesterone concentrations follow the changes of the corpus luteum closely.
* Progesterone concentrations follow the changes of the corpus luteum closely.
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===Uterine Cytology===
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This is often performed routinely before breeding commences on stud farms. Endometrial and inflammatory cells are examined. Evidence of bacteria in the absence of inflammatory cells is normally due to contamination.
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* Oestrus/Active Cycling
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** A high number of columnar epithelial cells with oval, basal nuclei containing finely stippled chromatin.
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** Columnar, finely vacuolated cytoplasm.
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** There should be no inflammatory cells or infectious agents visible. Rarely neutrophils may be present if it is a foal heat or the first oestrus cycle in maiden mares.
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* Anoestrus/Ovarian Inactivity
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** Clumps of epithelial cells with crowded or overlapping, oval, hypochromatic ‘bland’ nuclei without granular chromatin or nucleoli.
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** Unsubstantial cytoplasm with indistinct boundaries.