Progesterone profiles of 7 cycling gilts and those of 6 gilts inseminated on day 1 (1 day after the onset of oestrus) were studied. The results showed that plasma progesterone concentration in the inseminated group was higher (P<0.05) from day 14 onwards, indicating that the "rescue" of the corpus luteum (i.e. from luteolyis) for pregnancy occurs before day 14. In 1 of the inseminated gilts, the progesterone concentration declined on day 27, and the gilt returned to oestrus on day 30. The progesterone and oestrone sulphate profiles of this gilt indicated that the return to oestrus may have been caused by embryonic loss before day 14 after a 1st signal for corpus luteum maintenance has been generated. Another gilt aborted on day 27. The data on this gilt indicate that pregnancy failure may have been caused by a maternal malfunction.
van der Meulen, J., Helmond, F. A., & Oudenaarden, C. P. J. (1990). Corpus luteum function in the pig: progesterone profiles of cyclic and pregnant gilts. Netherlands Journal of Agricultural Science, 38(1), 45-52. https://doi.org/10.18174/njas.v38i1.16609