Dietary manipulation of local versus systemic progesterone and effects on embryo survival and litter size in gilts

Abstract

Progesterone is an important driver of endometrial function and as such plays an important role in early embryo development, implantation and survival. High feeding levels during early pregnancy in gilts usually result in a decrease in the concentration of progesterone in systemic blood circulation, through an increase in hepatic metabolism, and have as a consequence been associated with a reduction in embryo survival. However, effects of feeding level on embryo survival have been equivocal with some studies finding no, or even, positive effects of an increased feeding level on embryo survival. This paradox may be due to an underestimated supply of ‘local’ progesterone (directly from the ovary to the uterus), which may be enhanced at a higher feed level. This thesis proves the importance of the contribution of this local source of progesterone for embryo survival, using a unilateral ovariectomy model, and that progesterone concentrations in the venous drainage from the reproductive organs actually increases at higher feeding levels. Across all studies presented in this thesis a high feed level was not detrimental to embryo survival and was actually beneficial in some studies. Ovarian production of progesterone may also be increased in animals on a high feed level, and therefore progesterone transferred directly from the ovary to the uterus may add considerably to systemic progesterone supplied to the uterus, and counteract a reduction in systemic progesterone when gilts are fed at a high feed level. Furthermore, a high feeding level also seemed to be beneficial in terms of growth rate which is important in gilts as they are still growing towards their mature body weight and a higher growth rate was also positively correlated to pregnancy rate.