Uterine luminal proteins and estrogens in gilts on a normal nutritional plane during the estrous cycle and on a normal or high nutritional plane during early pregnancy

In gilts, a high plane of nutrition during early pregnancy often results in increased embryo mortality, possibly related to changes in embryo-uterine asynchrony at a critical stage of pregnancy (around Day 11). Therefore, in the present study, uterine luminal proteins and estrogens were studied between Days 5 and 16 after the onset of estrus in gilts on either a normal (2.5 kg/d, cyclic and pregnant gilts) or a high (4.0 kg/d, pregnant gilts only) feeding level. Conceptus recovery rate between Days 5 and 12 was not affected by the feeding level during early pregnancy, neither were systemic progesterone levels. Between Days 9 and 11, dramatic changes took place in the protein composition of the uterine luminal 10kD+ proteins, shifting from most (90%) of the acidic proteins at Day 5 and 7 to approximately 50% at Day 11/12, especially due to an increase in basic proteins with an iso-electrical point of more than 8. This shift occurred most rapidly for the pregnant gilts at the high feeding level and least rapidly in the cyclic gilts, resulting in significant differences in the relative amount of acidic proteins at Day 10 and 11 after the onset of estrus (P < 0.05). Similarly, levels of estrogens in the uterine flushings at Days 10, 11 and 12 were always highest for the pregnant gilts on the high feeding level and were always lowest in the cyclic gilts (P < 0.05); pregnant gilts on the normal feeding level showed intermediate estrogen levels. The fact that gilts on a high feeding level during early pregnancy show more rapid changes in the uterine luminal protein composition and embryonic estrogen production seems to suggest that the rate of these changes may be related to embryo survival.