The appearance and characteristics of early pregnancy factor in the pig.

The occurrence of early pregnancy factor 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. In the pig EPF is present virtually to the end of pregnancy, with a biphasic production in which the titres of EPF decline markedly in mid-pregnancy. Free EPF-A appears concurrently with EPF in the first 3 weeks 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.