Retention of tubal eggs in mares.

This research paper investigates the rates and factors of egg retention in the oviducts of horses, finding that eggs are commonly retained in mares, particularly heavy breeds, and more often in early pregnancy.

Study Sample

• The researchers examined the genital tracts of 227 mares. These mares were in different reproductive states, allowing for a comprehensive study on the occurrence of egg retention across a diverse sample.

Findings

• The researchers found eggs in the oviducts of 88.2% of the 212 non-pregnant mares included in their study. This shows that egg retention in mares, regardless of their pregnancy state, is quite common.
• The number of eggs retained in each mare ranged from none to 21, with an average of just over 4.
• Egg retention was found to occur more frequently in heavy breed mares compared to light breeds, suggesting that breed might be an influential factor in egg retention.
• Eggs were more frequently found in the oviducts during the early stages of pregnancy, indicating a possible relationship between the timing of pregnancy and egg retention.
• In contrast, no eggs were found in the oviducts of two anovulatory post-partum mares – those which did not ovulate after giving birth, reducing the likelihood of egg retention in such cases.

Related Observations

• The researchers also noticed the presence of globular masses in the distal region of the ampulla, which they believe may partially contribute to the retention of eggs. These masses likely consist of desquamated tubal mucosa, a substance that comes from the lining of the oviduct and may act as a blockage, causing eggs to be retained.