Advances in bovine reproduction and embryo technologyInfluence of progesterone on oocyte quality and embryo development in cows
Introduction
The steroid hormone progesterone (P4) plays a key role in reproductive events associated with establishment and maintenance of pregnancy. In cattle, approximately 40% of conception loss is estimated to occur from Days 8 to 16 of pregnancy (Day 0 = ovulation)[1], [2], [3]. Conceptus growth and development require the action of P4 on the uterus to regulate endometrial function, including conceptus–maternal interactions, pregnancy recognition, and uterine receptivity for implantation. A considerable proportion of embryo loss may be attributable to inadequate circulating P4 concentrations and the subsequent downstream consequences on endometrial gene expression and histotroph secretion into the uterine lumen. Furthermore, low P4 concentrations have also been implicated as a causative factor in the low pregnancy rates observed in high-yielding dairy cows [1]. Elevated concentrations of circulating P4 in the immediate post-conception period were associated with an advancement of conceptus elongation [4], [5], [6], an increase in interferon-tau production [7], [8], and higher pregnancy rates in cattle and sheep [9], [10], [11]. This review will summarize recent data highlighting the role of progesterone in determining oocyte quality and embryo development in cattle.
Section snippets
Effect of progesterone on the oocyte
The role of P4 in mammalian oocyte maturation and its potential impact on oocyte quality has not been well defined. However, the well-described switch from estradiol dominance to P4 dominance in the follicular fluid of preovulatory follicles in the period between the LH surge and ovulation [12], coincident with resumption of meiosis and maturation of the oocyte, suggests a role for P4 in this process. Injection of bovine preovulatory follicles with trilostane, an inhibitor of 3
Effects of progesterone on the endometrium
Preparation of the uterine endometrium for embryo attachment and implantation in all studied mammals, including ruminants, involves carefully orchestrated spatiotemporal alterations in transcriptomic profiles. Despite the importance of P4 for establishment and maintenance of pregnancy in mammals, paradoxically, endometrial epithelia cease expressing P4 receptors prior to implantation in all mammals studied [27]. The loss of P4 receptors in uterine epithelia appears to be a prerequisite for
Effect of progesterone on the embryo
The effects of elevated progesterone shortly after conception on the advancement of conceptus elongation have been convincingly demonstrated in cattle and sheep. Garrett et al [4] administered 100 mg progesterone on Days 1, 2, 3, and 4 of pregnancy which resulted in an increased peripheral plasma progesterone concentrations on Days 2 to 5 and significantly larger conceptuses on Day 14. Using a progesterone implant on Day 3 of pregnancy, Carter et al. [5] significantly elevated progesterone
Strategies to improve pregnancy rates through increasing P4
The beneficial effects of exogenous supplementation have been known for some time. Johnson et al [44] reported higher pregnancy rate to first service following 100 mg injections of progesterone on Days 2, 3, 4, 6, and 9 after AI (68%, 36/53) compared to controls (42%, 29/69). Robinson et al [45] reported higher pregnancy rates at Day 55 post insemination in lactating Holstein cows treated with a PRID from Days 5–12 (60.7%, 17/28) or Days 10–17 (59.2%, 16/27) compared to controls (30%, 9/30).
Conclusion
Clearly, P4 is a key player in the establishment and maintenance of pregnancy. It can indirectly affect the quality of the oocyte through its effects on LH pulsatility and the development of a persistent dominant follicle. Furthermore, it has a crucial role in creating an optimal uterine environment in which the embryo can develop, through its actions on the uterine endometrium, and in turn, the composition of the histotroph. Strategies aimed at elevating P4 in the early luteal phase have led
Acknowledgments
The author's work is supported by Science Foundation Ireland (Grants: 06IN1B62 and 07/SRC/B1156).
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