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Regular returns to estrus occur 18 - 24 days and 38 - 44 days post-service. A sow has a regular return (maintaining the normal duration of an estrous cycle: 18-24 days or its multiples) when fertilization of the eggs has failed or when all fertilized embryos have been lost within the first half of the estrous cycle (<10-12 days).
Under normal conditions these should make up a very small percentage of the matings, < 5%.
Among the possible causes we must distinguish between two major types:
Causes related to the semen dose (or boar) 
Use the buttons above or the flowchart to continue troubleshooting the returns to estrus, or access other parts of the tool.
