Comparison of plasma progesterone profiles in cyclic, pregnant, pseudopregnant and hysterectomized pigs between 8 and 27 days after oestrus.

Plasma progesterone concentrations were compared in cyclic (n = 12), pregnant (n = 12), oestradiol-induced pseudopregnant (n = 12) and hysterectomized gilts (n = 10) between days 8 and 27 after oestrus. The results were grouped into periods covering days 8-13, 14-20 and 21-27 and analysed by least-squares analysis of variance. Plasma progesterone concentrations were significantly (P less than 0.001) higher in hysterectomized compared with other groups between days 8 and 13. Progesterone concentrations declined rapidly after day 14 in cyclic females and gradually in the other groups. Throughout the third and fourth weeks the mean progesterone concentrations for hysterectomized animals were consistently higher than for pseudopregnant animals (P less than 0.05). The pregnant group means were below but not significantly different from the hysterectomized means in both of the last two periods. The greater progesterone concentrations in hysterectomized gilts indicated that secretion is high without any conceptus-produced or -mediated luteotrophic, and corpora lutea in cyclic, pregnant or pseudopregnant gilts may never reach full secretory potential.