Research to date has not been able to pinpoint a single cause of high sow mortality, but there seem to be some basic causative elements that can be recognized. Sow mortality continues to be a major challenge in breeding herds.

University of Minnesota swine veterinarian John Deen, DVM, PhD, says sow mortality is not only a real economic cost to producers, it is demoralizing to employees and their interaction with animals and it is a welfare concern because many of these mortality are the result of agonal processes.

Deen says that research studies to date have not been able to pinpoint a single cause of sow mortality. “Therefore the analysis and subsequent improvement must involve a complex of changes that will vary from farm to farm,” he says.

“Whether we analyze the causes through necropsy, epidemiology, or experimental interventions, the answers are not clear and forthcoming.”

Basic elements
At the same time, according to Deen, there are some basic elements that can be recognized. One of these, he says, is that the rates of sow mortality are very high during the first 20 to 25 days after farrowing. “Interestingly enough there is also another period of risk,” he says. “It is approximately 135 days after farrowing, which coincides with the subsequent farrowing event. These are sows that are due to farrow but die instead of farrowing at that point. Approximately 50 to 60 percent of sow mortality is commonly found in this time frame of shortly before farrowing to 21 days after farrowing.”

Deen says that sows seem to be more susceptible to a number of conditions during the farrowing and lactation period. An example would be porcine reproductive and respiratory syndrome (PRRS). “ Empirically, it appears that during this phase, sows are more likely to die during a PRRS outbreak,” he says. “We can argue that heavy lactation creates a high level of metabolic stress upon the sow. Secondary infections can occur both in the uterus and the mammary glands.”

Management factors?
Are there any specific management factors that might be addressed during this period that would help to reduce sow death?

To help answer this question, Deen points to a study that was done on the records of four Midwestern herds that had historically high sow mortality rates in the periparturient period. In all, the herds consisted of 10,500 sows that had a total of 17,117 farrowings and 514 periparturient deaths. The study further looked closer at a subset of 1,843 sows and 41 deaths.  Mortality rates in these herds were greater than 10 percent per year, explains Deen. “This translated into approximately 4 percent of sows that entered the farrowing crate died before leaving.”

Researchers are currently reviewing preliminary results of this study in an effort to further identify some important factors that are important in managing the sow, Deen says. The following management factors and/or risks associated with high mortality have been identified so far:

1. Lameness. In Deen’s research, lame sows entering the farrowing crate had a 40 percent higher chance of dying subsequent to farrowing. “One of the research factors that we are monitoring is whether or not a sow gets up immediately after farrowing. This is correlated with drinking and eating and the lack of farrowing problems. Anything that impedes the sow from getting up easily has to be a concern. One of our current questions is whether analgesia may be useful post-farrowing.”

2. Season and lack of cooling. The research shows that sows tend to die at a higher rate during the summer, with the risk of mortality being approximately 38 percent higher from June to
September than other months. High temperature is a concern for farrowing sows, says Deen. At the same time, he says, “‘hot’ is a relative term, it appears. The optimal temperature for a farrowing sow is below 60°F. This is a temperature rarely seen, especially for the latter sows farrowing within a room. Heat exhaustion and dehydration are not uncommon clinical signs seen in sows after farrowing.” In the research, on days when the ambient temperature exceeded 90°F, the risk of sow mortality just about doubled.

3. Lack of water. Deen says the water requirements of a lactating sow (in particular, a sow immediately post-farrowing) can be quite high. “High‑volume, low‑pressure water nipples are needed to deliver water quickly to sows that are unlikely to stand for a long time. Fluctuating water pressure levels inside barns can be a concern as the needs of a sow post-farrowing are immediate, and waiting for the pressure washing to be finished is not a good strategy.” In the study, not getting up and drinking in the subsequent feeding time had an 18 percent higher risk of mortality.

4. Parity. In the study, sows of three parities or less had a 26 percent higher mortality risk than older sows.

5. Infectious diseases. “Normally we have thought of sows as being quite robust and insensitive to the effects of diseases such as influenza, PRRS and respiratory pathogens. Yet anything that puts a lactating sow off feed should be a concern.”

6. Litter size. Larger litters (>12) seem to be protective to sows. In the study, there was a 7 percent decrease in the risk of a sow dying.

7. Stillbirths. Compared with litters with no stillbirths, sows with stillbirths have a 27 percent higher likelihood of dying. Deen says it “is surprising that mortality is substantially higher in sows that have stillbirths, particularly more than one stillbirth. Though we have often focused on stillbirths as an economic problem to itself, it is the effects on sows that may be more of a concern. Part of the answer is to ensure that sows are checked regularly during the farrowing process. More importantly, we need to identify those sows that are at risk of stillbirths and provide better care.”

8. Induced farrowing. Induced farrowing increased mortality risk by about 39 percent in this study. Oxytocin was not used as part of the induction process in the study. Induced farrowing, says Deen,  demands extra attention for sows. “In our analyses, induced sows continued to have higher mortality rates than those not induced, especially when we control for day of week effects. There is a weekend effect that tends to increase mortality as well, but simply farrowing sows during the week without extra attention may not be the answer.”

9. Obstetrical assistance. In the research, obstetrical interventions and duration of farrowing, when controlled for stillbirths, did not have an effect on mortality. But when obstetrical assistance was examined independently, it showed an increase in the likelihood of mortality by approximately 31 percent, says Deen.

10. Day of the week. “Sows farrowing on the weekend had approximately a 9 percent increase of likelihood of dying during that periparturient period,” Deen reports.

11. Feed intake. “Two or more days of insignificant feed intake during the first week post-farrowing signified a problem sow and the sows had a higher level of mortality.” In the study, the odds of mortality were increased by 31 percent, says Deen.

12. Farrowing crate acclimatizing. Acclimatizing to the farrowing crate, when controlling for gestation length, had no effect on mortality.

13. Backfat. Sow condition scores were a better predictor of mortality than backfat in this study.

14. Farm differences.  In the study, there were differences between farms even when accounting for some of the above-mentioned factors. For example, one farm had a lower risk of mortality of approximately 31 percent in comparison to the other farms.

Deen says the above factors taken together signify a problem sow. “It appears that certain sows exposed to a combination of factors can have mortality rates as high as 35 percent in a single farrowing.”

He adds that “further analysis must be done with a larger number of herds to identify in more detail the problems seen in these animals.”

Deen acknowledges that “sow mortality is a difficult area to study. It is a relatively infrequent event and appears to involve factors that may precede the death by months or even years. Realizing this, it is important to come to a better understanding of risk factors involved in creating a sow that is at a higher risk of mortality. It is also unlikely that risk factors operate independently, and there may be multiplicative effects that are most important. Conversely, it is also a reason that experimental interventions studies are unlikely to come to a final conclusion for mortality control.”

Deen concludes that sow mortality management needs to address the aim of creating a robust sow that is resistant to many of the challenges of weaning multiple litters in the face of additional challenges of disease, temperature, obstetric complications and other factors. “At the same time, we must minimize the challenges for these sows to not overwhelm their abilities to adjust to challenges.”

Control of mortality, says Deen,   is an incremental process. “It is a long process that takes a number of measurements and often an intuitive approach to understanding the multiple insults to which a sow can be exposed, and the methods of creating a robust sow. Treatment can be difficult and prevention is probably a better strategy.”   

Editor’s note: John Deen is a swine veterinarian at the University of Minnesota Swine Center, who presented the information from which this article is based at last summer’s University of Nebraska George A. Young Swine Conference in South Sioux City, Neb.