Superfetation

One possible reason for delayed implantation of the embryo (see Delayed Implantation 01-05-22) is superfetation.

Superfetation is when a female continues ovulation after successful breeding until the end of its breeding season. That is, a female can ovulate and conceive again even while pregnant.

An example of delayed implantation due to superfetation is the mink (Mustela vison). During the breeding season mink females mate with multiple males over a period of time. The fertile egg resulting from each successful mating develops to the blastocyst stage then suspends development and floats in the uterus until the breeding season is over. Once the breeding season is over all the blastocysts in the uterus implant at the same time so that all the young are born together and can be raised together. This is definitely easier on the parent mink than having offspring arrive serially.

This mink was photographed along the Big Lake Levee near McArthur CA (Shasta County).

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