Composition of the bovine uterine proteome is associated with stage of cycle and concentration of systemic progesterone.

Early embryonic loss accounts for over 70% of total embryonic and foetal loss in dairy cattle. Early embryonic development and survival is associated with the concentration of systemic progesterone. To determine if the uterine proteome is influenced by stage of cycle or systemic progesterone concentrations, uterine flushings were collected from the ipsi- and contralateral uterine horns of beef heifers on Days 7 (n = 10) and 15 (n = 10) of the oestrous cycle. Animals were separated into low or high progesterone groups based on plasma progesterone concentrations on Day 5 of the cycle. Samples were albumin depleted before iTRAQ R labeling and subsequent strong cation exchange-LC-MS/MS analyses. A total of 20 proteins were up to 5.9-fold higher (p<0.05) and 20 were up to 2.3-fold lower on Day 15 compared toDay 7. In addition, the expression of a number of proteins on Day 7 and/or 15 of the cycle was correlated with progesterone concentrations during Days 3–7 or the rate of change in progesterone between Days 3 and 7. This study highlights the dynamic changes occurring in the microenvironment surrounding the embryo during this period. The findings here also support the hypothesis that progesterone supports embryonic development by altering the maternal uterine environment.