PubMed1992
Stillbirths, mummies, abortions, and early embryonic death have a substantial impact on the profitability of a farm in both endemic and epidemic conditions. Fetal death is highly dependent on stage of gestation. Implantation occurs around day 14 postmating in sows, and fetal death of an entire litter at this time usually results in a regular return to service. If more than four embryos remain alive, the sow may go on to farrow normally. If fetal death occurs after implantation but before calcification (around 35 days gestation), the sow will either return to estrus at an irregular interval or will farrow a normal litter of reduced size. Although fetuses are normally resorbed prior to calcification, fetal death after that stage of development leads to mummification. Abortions are more directly related to maternal control of pregnancy than fetal failure. Stillbirths are those pigs that appear normal at birth but have lungs that do not float in water. Causes of fetal death can be divided into infectious and noninfectious categories. Infectious causes perhaps are overemphasized but are certainly important in epidemic situations. Some infectious causes of fetal death are primarily systemic maternal pathogens, whereas others may attack the fetus and/or placenta, directly such as PPV, PEV, PRV, SIRS virus, and Leptospira sp. Several other infectious agents have been associated with fetal death. Noninfectious causes of stillborns, mummies, abortions, and early embryonic death are most common in endemic situations. Most stillbirths are due to difficulty at or around parturition, primarily extended duration causing fetal anoxia. Environmental factors such as increased ambient temperature and seasonal infertility affect death rates, as do specific individual sow characteristics, nutritional factors, and toxicities. The causes of stillborns, mummies, abortions, and early embryonic death are often difficult to ascertain, but the potential rewards make investigation efforts worthwhile.