By Billy Flowers, North Carolina State University
While the emphasis for most sow farms is on number of pigs born alive as it should be, sometimes, the ones that aren’t born or are born dead — stillborns and mummies — provide better clues as to where management can improve.
Any embryonic losses that occur between days 15 and 40 are totally reabsorbed by the sow. This is a normal process as pregnant sows try to neutralize dead and dying tissue in order to protect embryos that are still alive. Mummies (or mummified fetuses to be anatomically correct) are fetuses that die anytime between days 40 and about 100 of gestation. They are born partially decomposed because the same mechanisms discussed previously that are part of the normal detoxification process also attempt to neutralize dead fetuses.
The difference is that calcification of the cartilaginous fetal skeleton has progressed to a point where the sow can decompose the soft tissues, but not the calcified bone, thus, resulting in the “mummified” appearance.
Stillborns are fully formed pigs that are born dead. They die either late in gestation, after day 100, or during farrowing when they suffocate as they traverse the birth canal. They typically aren’t in the uterus for very long, so there isn’t much of an opportunity for the uterus to breakdown the soft tissue.
This information can be used very effectively to assist with determining when and what type of management factors during gestation and/or farrowing might be affecting the sow and her pregnancy in a negative manner.
This is illustrated in Figure 1. When most of the death loss occurs between days 15 and 40, assuming there aren’t significant problems with semen quality or insemination techniques) one would expect the total number of pigs born to be low since all the dead embryos would be reabsorbed.
Figure 1: Relationships among litter characteristics of total number of pigs born, mummies and stillborns and timing of death losses during pregnancy.
In contrast, the number and size distribution of mummified fetuses within a litter is very useful in determining when and, to some extent, what type of stresses affected the sow between days 40 and 100 of pregnancy. If the mummies are all fairly consistent in size, then this typically is due to an acute stressor that affected the sow relatively over a short time interval such as heat stress, fighting after mixing sows in pen gestation systems and some diseases. If the mummies within the litter vary in size from small and highly decomposed to large and mostly intact, then this usually is representative of a chronic stressor which has occurred over a long period of time. The smallest fetuses are the most vulnerable so they die first, but over time the larger ones also are affected as the stress persists. In theory, any acute stressor also can be a chronic stressor if it occurs at a reduced magnitude over a longer period of time. The most common examples are exposure to high humidity and temperatures in the upper-70 degrees Fahrenheit for several months as is common during the summer and diseases such as porcine reproductive and respiratory syndrome when sows are infected early in gestation.
In some situations, the presence of small mummies may not be related to negative management conditions. Highly prolific sows usually have more embryos after breeding than their uteri can support during pregnancy. Consequently, it isn’t unusual for these sows to lose some fetuses shortly after implantation. These most likely would either be completely reabsorbed or become small mummified fetuses depending when they die in utero relative to day 40 of gestation. Litters such as these from time to time probably aren’t a cause for alarm. However, if the frequency and size of mummies increases, then there probably is some type of stressor present during mid-gestation.
A close examination of the color of stillborn piglets can provide clues as to whether the pig died late in gestation or during farrowing after parturition began. Stillborns with a brown, greenish color most likely died during farrowing. The material that often stains the skin is remnants of fetal waste produced during gestation and stored in fluid-filled sacs that surround the fetus. Once farrowing begins, powerful uterine contractions rupture the fluid-filled sacs and push the fetus out of the uterus and through the rest of the birth canal, hopefully, without any problems.
Stillborns (and live piglets) with discolored skin are ones that, at some point, got stuck or were retained in the uterus after the fluid-filled sacs containing the fetal waste ruptured. This is why their skin is stained. Increased attention to observing sows during farrowing and providing assistance when needed is in order. In contrast, stillborns that died prior to the onset of farrowing, in most cases, do not have any discoloration of the skin — they died during gestation, but were delivered normally. In this situation, examination of how sows were handled the last week of pregnancy, especially their movement from gestation to farrowing barns is warranted.