Causes of irregular returns to estrus

Irregular returns to estrus occur from 25 to 37 days post-service. A sow has an irregular return (abnormally long estrous cycle) when all the embryos have been lost (< 35 days of gestation) and are reabsorbed, or when only 5 or fewer embryos remain at 10 days of gestation.

Under normal conditions, these should account for a very small percentage of the matings < 3%.

Irregular returns are generally considered to be a problem when they account for more than 30% of the total returns, but it should be noted that when the total returns are very low, irregular returns will account for a higher percentage of the total, and this is considered normal, as the problem sows are those that return (we are not up against a problem).

Among the possible causes we must distinguish two major types:

Infectious causes

Non-infectious causes

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