The appearance and characteristics of early pregnancy factor in the pig

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Abstract
The occurrence of early pregnancy factor [EPF; pregnancy-dependent protein complex] in the pig has been established by the rosette inhibition test and by the criteria that gel filtration of serum resulted in a number of peaks of activity similar to those observed in other species [human, mouse, sheep]. In the pig EPF is present virtually to the end of pregnancy, with a biphasic production in which the titers of EPF decline markedly in mid-pregnancy. Free EPF-A [separate moiety formed in the oviduct] appears concurrently with EPF in the first 3 wk of pregnancy in some but not all pigs. The presence of excess EPF-A has an inhibitory effect in the rosette inhibition test and modifications, including an initial serum dialysis step, have been introduced into the test to take account of this inhibitory effect.