* Depends on the phase of the oestrous cycle and whether it contains an active corpus luteum.
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* The presence of follicles does not alter the size of the ovary to anything like the extent of the corpus luteum.
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* In the majority of heifers and young cows examined between day 6-18 of dioestrus, one ovary will be larger than the other.
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* The larger ovary will be approximately:
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** 3.5cm pole-pole
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** 3cm from the attached side to the free border
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** 2.8cm from side to side
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** The corpus luteum will project from some point on the surface.
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* The smaller ovary will be approximately:
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** 2.5cm pole-pole
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** 1.5cm from the attached side to the free border
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** 1.2 cm from side to side
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* During the 4-5 days after oestrus, the developing corpus luteum has not attained sufficient bulk to influence the size of the ovary significantly and the regressing corpus luteum has lost significant bulk.
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* During oestrus there will also be little difference in size.
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** If the ovary undergoing enlargement of a dominant follicle also contains a regressing corpus luteum, it will be a little larger than the other ovary but not strikingly so.