Causes of regular returns to estrus

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)

Causes related to the sow

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