Pregnancy Failure in Animals

Pregnancy failure refers to the inability of a pregnancy to establish or progress to full term, resulting in the loss of the embryo or fetus at any stage.

It can occur due to a variety of factors, including fertilization failure, early embryonic death, fetal death, hormonal imbalances, infections, nutritional deficiencies, genetic abnormalities, or environmental stress.

Pregnancy failure may be divided into two main sections:

1. Failure to Establish Pregnancy
2. Failure of an Established Pregnancy

Failure to Establish Pregnancy

Unattached conceptuses within the uterus are susceptible to damage by many factors. Where pregnancy fails around the time of maternal recognition of pregnancy (i.e. around days 12-13) sows tend to return to estrus outside the normal range for ‘regular returns’

The problem may be associated with failure of maternal recognition of pregnancy related to:

• Stress
• Infectious challenge

Failure of pregnancy at this stage may be total (resulting in an irregular return to service) or partial (resulting in resorption of some embryos, and consequent reduction in litter size)

Failure of an Established Pregnancy

Death of conceptuses during the embryonic stage tends to result in resorption if abortion does not occur.

Dissolution of embryos in the absence of anaerobic bacteria is an aseptic, autolytic process resulting in complete disappearance of the products or a vaginal discharge. Reduction in numbers born due to partial resorption of litter will be the only presenting sign.

Once pregnancy has been confirmed (e.g. by the Doppler ultrasound technique on days 28-35), fetal death is more likely to result from an infectious disease.

Beyond 35 days, fetal death will result in mummified fetuses at farrowing. Mummification is the most common clinical manifestation of a viral infection (e.g. Aujeszky’s disease, porcine parvovirus, porcine reproductive respiratory syndrome or swine fever) at this time, although only a proportion of the fetuses may be affected.