Effects of the Estrous Cycle and Early Pregnancy on Bovine Uterine, Luteal, and Follicular Responses1

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Abstract
Uterine, luteal, and follicular responses associated with the estrous cycle and early pregnancy in cattle were examined. Dairy (n=19) and beef (n=19) cattle were slaughtered either on Day 4, 8, 12, 14, 16, or 19 postestrus (estrus = Day o). Corpus luteum (CL) weight, specific PGF2α binding by the luteal particulate fraction (100,000 × g pellet), in vitro estradiol (E2) production by the two largest follicles, total recoverable uterine luminal protein (TP), total recoverable immunoreactive uterine luminal PGF (TPGF), and peripheral plasma steroids were evaluated. In a parallel study, beef cattle (n=22) were slaughtered either on Day 8, 12, 14, 16, or 19 of pregnancy for measurements of TP, TPGF, and plasma steroids. Uterine luminal proteins, from cyclic and pregnant cattle (Day 19), were subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) for determination of protein molecular weights and protein profile characterization. In cyclic cattle, CL regression was not completed by Day 19. Follicle E2 secretion varied among animals within day (X̄ = 4.0–24.0 ng E2/follicle/3.5 h; P2α binding (fmole/CL) for Days 4, 8, 12, 14, 16, and 19 was 14.29, 145.79, 177.34, 111.82, 174.51, and 199.17 (PMr range × 10-3 = 18.7 to 292.0). Proteins appeared with greater frequency later in the cycle than earlier (Days 14, 16, 19: 60% vs Days 4, 8, 12: 45%). Composite SDS-PAGE profiles from Days 8–12 and Days 14–16 differed (P2α binding sites in the CL. Higher PGF in utero at Days 16 and 19 of pregnancy and changes in TP and SDS-PAGE protein profiles may reflect responsiveness of endometrium to changes in ovarian status (cyclic) and/or conceptus activity (pregnancy comparisons).

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