Physiology and pathology of embryonic mortality in cattle

Normal maintenance of pregnancy

Relationship between oestradiol and progesterone levels in pregnancy maintenance

It has been recently proven that the relationship between progesterone and oestradiol in circulation during the first two week post insemination play a crucial role in the maintenance of luteal function and therefore pregnancy itself.

A new wave of ovarian follicles grows during the luteal phase, even if fertilisation has been successful. If oestradiol production of these growing “luteal phase” follicles in not diminished early enough, luteolysis is triggered and corpus luteum resolved.

Prevention of luteolysis in a pregnant cow:

  • increasing progesterone concentrations exert negative feedback, inhibit gonadotrophin release leading to decreasing oestradiol production
  • interferon tau secreted by developing embryo interferes with the luteolytic cascade at endometrial level

Figure 1: Maintaining pregnancy

maintaining pregnancy

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Failure to maintain pregnancy

Why does the system fail?
In high producing dairy cows and in some infectious diseases such as BVDV infection, circulating levels of progesterone are too low to prevent luteolysis.

Evidence from the literature
Mann and Lamming (2001) evaluated progesterone and oestradiol concentrations in inseminated cows and noted the presence or abscence of an embryo on day 16 post AI.

  • Plasma E2 concentrations were significantly higher in the embryo negative group than in the embryo negative or control group on day 1 and also higher than in embryo(+) group on days 2 and 3.
  • Cows in embryo (-) group had significantly delayed increase in progesterone concentrations after ovulation (day 6.2) in comparison with embryo (+) group (day 4.9) and control group (day 5)
  • The overall progesterone concentrations during luteal phase was lower in the embryo (-) group than in embryo (+) group

Causative Factors:

  • Poor quality of the oocyte (impaired follicular development, delayed ovulation)
  • Disrupted and abnormal fertilisation
  • Embryonic chromosomal abnormalities
  • Unfavourable changes in uterine environment (endometritis, increased blood urea levels)
  • Diseases inducing fever
  • Heat stress
  • Inadequate progesterone levels:
    • impaired luteal function (NEB, infectious causes, heat stress)
    • increased metabolism of progesterone in highly producing dairy cows
  • Precocious luteolysis
  • Direct effect of some infectious agents (BVDV, IBRV etc.)

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