Abstract
Progesterone (P4) from the corpus luteum (CL) is critical for the establishment and maintenance of pregnancy and plays a major role in regulating endometrial secretions essential for stimulating and mediating changes in conceptus growth and differentiation throughout early pregnancy in ruminants. Numerous studies have demonstrated an association between elevated P4 and acceleration in conceptus elongation. A combination of in vivo and in vitro experiments found that the effects of P4 on conceptus elongation are indirect and mediated through P4- induced effects in the endometrium. Despite effects on elongation, data on the impact of post-insemination supplementation of P4 on pregnancy rates are conflicting and typically only result in a modest improvement, if any, in fertility. Differences in conceptus length on the same day of gestation would suggest that factors intrinsic to the blastocysts transferred regulate development, at least in part, and would be consistent with the hypothesis that the quality of the oocyte regulates developmental competence. This paper will review recent knowledge on the effect of P4 on conceptus development in cattle and summarize strategies that have been undertaken to manipulate post fertilization P4 concentrations to increase fertility.
Highlights
Most embryonic loss in cattle occurs in the first few weeks after conception
The majority of these embryos are lost between fertilisation and maternal recognition of pregnancy, which in cattle occurs around day 16 post-mating (Diskin and Morris, 2008; Wiltbank et al, 2016)
This study found that P4 supplementation advanced the normal temporal changes in endometrial gene expression, for genes associated with energy sources or contributors to histotroph, which may contribute to advanced conceptus development on day 13 and day 16
Summary
Fertilisation success is typically high (~90%) but a significant proportion of the resulting embryos fail to develop to term The majority of these embryos are lost between fertilisation and maternal recognition of pregnancy, which in cattle occurs around day 16 post-mating (Diskin and Morris, 2008; Wiltbank et al, 2016). Optimal dialogue between the developing embryo and its mother is essential for successful pregnancy recognition and maintenance of pregnancy during the critical peri-implantation period of pregnancy when the stage is set for implantation and placentation that precedes fetal development (Guillomot, 1995; Hue et al, 2012; Spencer et al, 2015). Rather than repeat in detail what has already been written, the reader is directed to several other recent comprehensive reviews on the subject (Lonergan, 2011, 2015; Wiltbank et al, 2014; Spencer et al, 2015)
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