Understanding Sow Mortality

Kenneth Stalder,1 Ph.D.; Locke Karriker, 1DVM; Anna Johnson,1 Ph.D. Iowa State University, Ames, Iowa


Due to historically high feed prices and relatively low prices for market hogs, U.S. profit margins will continue to shrink .U.S. commercial pork producers need to continue to focus on improving production efficiency and improving sow mortality. To comprehend the current sow mortality levels it is important to have a historical perspective and reference.

Consumer demand for lean pork products has resulted in the buying systems of many pork processors to place a great deal of financial reward for carcass leanness and muscling over the past two to three decades. The way that sows are housed during gestation and lactation has moved towards more intensive systems so that sows can be more consistently managed and production maximized.

However, that too is changing with housing legislation in many European countries and with recent marketing strategies in the U.S. At a minimum, some of these factors have contributed to a rise in the average sow mortality experienced by many commercial sow herds in the U.S. Sow mortality is a contributing factor to the relatively low average number of parities a sow remains in the breeding herd of U.S. commercial sow herds.  A sow remaining in the breeding herd for fewer parities will wean and sell fewer pigs over her productive lifetime.  

PigCHAMP 2007 Mortality Results

One of the best data sets to benchmark your farms’ values against for various data point is the yearly PigCHAMP summaries. In the 2007 PigCHAMP summary we are focusing on sow mortality. The average sow mortality from 372 sow farms was 8.76 %. The amount of variation among the herds can be measured several ways. First of all, a range of sow mortality values observed in the 2007 PigCHAMP summary ranged from 1.4% to  22.7%. As is the case with all data, one must use caution as there are a variety of factors that can influence these values like farm size, type of gestation system, etc. These values clearly illustrate the extremes that can be seen on individual farms for sow mortality. This farm might consider trying to get below 10 or even 15% as an initial goal. In this manner goals are clearly achievable and can be adjusted once initials goals are met. Furthermore, there can be a variety of causes for high mortality rates that can be difficult to avoid. A classic example of this is a case where a disease causing organism enters the breeding herd and has a devastating impact on sow mortality rates. Of course, many herds try to avoid getting these types of diseases through proper vaccination programs and strict biosecurity procedures. However, occasionally even with our best efforts, livestock operations have a disease challenge and the associated negative impacts on production parameters occurs. Often the severity of any disease challenge can be limited by excellent animal care and treatment.

Another way to evaluate the variation that exists among the herds in the 2007 PigCHAMP summary is by determining the standard deviation for the trait. In this case the standard deviation for the 2007 PigCHAMP mortality rate was 3.22. 

  • Expect 66% of the mortality values to fall within + or – 1 standard deviation or between 5.6 and 11.9%

  • Expect 86 % of the mortality values to fall within + or – 2 standard deviations or 2.38 and 15.1.

  • Expect 95% of the mortality values to fall between 0 and 18.3%.
From the present data, 4 herds had a reported mortality rate above 3 standard deviations from the mean indicating they clearly have room to improve. On the other hand, 43 herds in this data set or 11.65 of the herds have a sow mortality rate below 5% Two-thirds or 66% of the herds in the 2007 PigCHAMP summary have a sow mortality rate below 10%. Furthermore, the top 10% of the herds for sow mortality have an average sow mortality rate of 4.7%. Therefore, producers that wish to benchmark themselves against the best 10% of producers having an average sow mortality rate of 4.7%. 

When compared to other countries participating, the average U.S. mortality rate of 8.8% is better than the average mortality rate of herds in Canada (9.5%; range 1.3 to 16.1%) The average mortality rate among PigCHAMP users from Spain was 9.9% (range: 2.1 to 17.7%).

The range in sow mortality rates from the three countries where sufficient data are available to make general comparisons are quite similar. Readers should keep in mind that the number of reporting farms in 2007 using PigCHAMP is much smaller from Canada (only 14 herds reporting) and Spain (only 57 herds reporting). Whereas, the number of herds in the U.S. data set is 370.


Sow mortality rates have been increasing in commercial swine herds over the past decade. Yet as seen by the 2007 PigCHAMP data summaries, many pork producers perform exceedingly well when evaluating breeding herd female mortality rates. Sow mortality of 10% or more is unacceptable.

Sow mortalities can make up a substantial portion of sows removed from the breeding herd on an annual basis. Further, annual sow mortality rates have been gradually increasing in the past 10 to 15 years (Irwin and Deen, 2000; Duran, 2001). Sow mortalities as a percentage of total breeding herd females, can commonly reach 10% or higher (D’Allaire, et al., 1987; Stein et al., 1990; Pederson, 1996).

When evaluating the reasons for sow mortality, the common causes for sow death which have been reported in the scientific literature include torsion and other abdominal organ injuries, heart failure, and cystitis (D’Allaire and Drolet, 1999). Common reasons for sow deaths from various research studies are summarized in Table 1. Evaluating the scientific literature for sow mortality causes by parity by parity, locomotion or leg related problems including arthritis, pneumonia, ulcers, and endometriosis tend to be associated with gilts and young sows. Heart failure, cystitis, uterine prolapse and torsion tend to be the more common mortality reasons reported for older sows (D’Allaire et al., 1987; Chagnon et al., 1991; Maderbacher et al., 1993). It has been shown that similar sow mortality challenges still exist today (Table 2).

A clear seasonal affect on sow mortality has been reported in the scientific literature. Typically, sow mortality increases during months where hot temperature and high humidity levels occurs (Chagnon et al., 1991; Drolet et al., 1992; D’Allaire et al., 1996; Deen and Xue, 1999; Irwin et al., 1999). Further, the peripartum appears to be a time when a high proportion of sow deaths occur (Chagnon et al., 1991; Deen and Xue, 1999; Duran, 2001; Deen, 2003;).

As with many challenges facing pork producers, management and housing appear to contribute to the underlying causes for breeding herd female mortality. It has been reported that rough handling and movement can play a role in abdominal torsion (Morin et al., 1984). Further, feeding management including how often the sows are fed and dietary changes in the make up of the lactation and gestation rations appear to play a role in the occurrence of gastric torsion (Morin et al., 1984; Sanford et al., 1984). More specifically, it has been reported that providing three meals per day decreases the risk of mortality when compared to feeding twice per day (Abiven et al., 1998).

The occurrence of heart failure among breeding herd females is typically associated with stressful events. The scientific litter has associated the peripartum period with the incidence of heart failure (Drolet et al., 1992) with nearly two-thirds of sow mortalities occurring as a result of cardiac failure taking place during this time period. This same study reported that other stressful events like fighting, mating, transport, elevated temperature, and other similar activities which sows typically encounter can contribute to an increased prevalence of cardiac failure. This same study suggests that increases in heart size have not kept pace with increased mature body size of modern lines of pigs and may need further evaluation.

While some management factors appear to increase breeding herd mortality rates, while others can lower the mortality risk. Some of the reported management factors include weaning pigs at an older age (28 days or greater), having a smaller litter size at birth (12 piglets or less), reaching maximum daily lactation feed intake before the 15th day of lactation, and having maximum daily feed intake at less than 8 kg. One research report (Brandt et al., 1999) found that females with the largest body size have an increased mortality risk between the third weaning and parity five. This work is supported by the findings of Deen and Xue (1999) and Tiranti et al. (2003) who reported that mortality risk increased as parity increases. Additionally, Brandt et al. (1999) found that poor leg quality scores of gilts also significantly impacted survival rates. This is of particular interest to the authors of this paper as the increased us of artificial insemination and increased emphasis on lean content of modern genetic lines can contribute animals with higher rates of feet and leg soundness problems. Studies which utilized PigCHAMP data (Koketsu, 2000) found that higher annual sow mortality rates was associated with larger herd size, increased parity at farrowing, shorter lactation length, and summer season which continues to support the findings of several earlier studies. In this study, increasing herd size by 500 sows resulted in an increased mortality risk by approximately 0.5%.

Sow mortality can have a large economic impact on commercial pork operations which experience relatively high mortality levels. Many of the sow mortalities occur after substantial costs have already been incurred by the pork operation. Schultz et al. (2001) reported that 38-40 percent of sow deaths occurred 100 to 125 days post breeding, a time at which a substantial gestational economic investment had already been made. Considering the relatively high feed costs experience by producers today, the cost of sow mortalities occurring this late in gestation is magnified.

Necropsy evaluation of numerous sows that have died is essential to accurately determining specific reasons for their occurrence on an individual herd basis (D’Allaire et al., 1992). Standardized protocols (Rueff, 2000) and diagnostic approaches (Pretzer et al., 2000) have been developed that allow a systematic determination of mortality causes within herd and across numerous herds. Clearly, the period immediately following parturition is the period when sows are at the greatest risk of death (Deen and Xue, 1999). This period of the sow’s life cycle should receive particular attention for personnel working in the farrowing area in order that mortality risk can be reduced in herd that are experiencing mortality levels requiring action.


High sow mortality in commercial pork production systems can lead to economic inefficiency and animal well being concerns because animal agriculture is under increasing scrutinizing from a variety of internal and external sources. The economic concerns of poor sow mortality rates arise from the fact that it can contribute to sows remaining in the breeding herd for fewer parities. Thus a sow in the herd for fewer parities will produce fewer pigs when compared to a sow that remains in the breeding herd for a longer period of time. 


1 Abiven, N., H. Seegers, F. Beaudeau, A. Laval, and C. Fourichon. 1998. Risk factors for high sow mortality in French swine herds. Prev. Vet. Med. 33:109-119.
2 Brandt, H., N. von Brevern, and P. Glodek. 1999. Factors affecting survival rate of crossbred sows in weaner production. Livest. Prod. Sci. 57:127-135.
3 Chagnon, M., S. D’Allaire, and R. Drolet. 1991. A prospective study of sow mortality in breeding herds. Can. Vet. J. 55:180-184.
4 D’Allaire, S. and R. Drolet. 1999. Culling and mortality of breeding animals. In: Diseases of Swine 8th Edition, B. E. Straw, S. D’Allaire, W. L. Mengeling, and D. J. Taylor Editors, Iowa State University Press, Ames, IA, 50011, pp. 1003-1016.
5 D’Allaire, S., R. Drolet, and D. Brodeur. 1996. Sow mortality associated with high ambient temperatures. Can. Vet. J. 37: 237-239.
6 D’Allaire, S., A. D. Leman, and R. Drolet. 1992. Optimizing longevity in sows and boars. Vet. Clin. North Amer. 8:545-557.
7 D’Allaire, S., T. E. Stein, and A. D. Leman. 1987. Culling patterns in selected Minnesota swine breeding herds. Can. J. Vet. Res. 51:506-512.
8 Deen, J. 2003. Periparturient mortality. In: Proceedings of the Allen D. Leman Swine Conf. 30:203-204.
9 Deen, J., and J. Xue. 1999. Sow mortality in the U.S.: An industry-wide perspective. In: Proceedings of the Allen D. Leman Swine Conf. 26:91-94.
10 Drolet, R., S. D’Allaire, and M. Chagnon. 1992. Some observations on cardiac failure in sows. Can. Vet. J. 33:325-329.
11 Duran, C. O. 2001. Sow mortality. Comp. Cont. Ed. Prac. Vet. 23:S76-S83.
12 Irwin, C., and J. Geiger, and J. Deen. 1999. Getting a handle on sow mortality. In: Proceedings of the North Carolina Healthy Hogs Seminar. Available at: http://mark.asci.ncsu.edu/HealthyHogs/book1999/irwin.htm Accessed: 1, April, 2008.
13 Koketsu, Y. 2000. Retrospective analysis of trends and production factors associated with sow mortality on swine-breeding farms in USA. Prev. Vet. Med. 46:249-256.
14 Maderbacher, R., G. Schoder, P. Winter, and W. Baumgartner. 1993. Causes of pig losses in a pig breeding unit. Deutche Tierarztliche Wochenschrift 100:468-473.
15 Morin, M., R. Sauvageau, J.-B. Phaneuf, E. Teuscher, M. Beauregard, and A. Lagace. 1984. Torsion of abdominal organs in sows: a report of 36 cases. Can.Vet. J. 25:440-442.
16 Pedersen, P. N. 1996. Longevity and culling rates in the Danish sow production and the consequences of a different strategy of culling. In: Proceedings of the Nordiska Jordbruksforskares Forening Seminar 265-Longevity of Sows. Ed. V. Danielsen, Denmark: Research Centre Foulum, pp. 28-33.
17 Pretzer, S. D. C. K. Irwin, J. O. Geiger, and S. C. Henry, 2000. A standardized protocol to investigate sow mortality. J. Swine Hlth. Prod. 8:35-37.
18 Rueff, L. 2000. Diagnostic approaches to reproductive failure in pigs. J. Swine Hlth. Prod. 8:285-287.
19 Sanford, S. E. G. K. A. Josephson, and A. J. Rehmtulla. 1994. Sudden death in sows. Can. Vet. J. 35:388.
20 Schultz, R. D. Dau, W. Cast, D. Hoefling, O. Duran, T. Carson, L. Becton, C. Woodward, K. Pollard, K. Busker, D. Kaster, and M. Steidinger. 2001. A sow mortality study – the real reasons sows die; Identifying causes and implementing action. In: Proceedings of the 32nd Annual Meeting of the American Association of Swine Practitioners, pp.387-395.
21 Stein, T. E. A. Dijkhuizen, S. D’Allaire, and R. S. Morris. 1990. Sow culling and mortality in commercial swine breeding herds. Prev. Vet. Med. 9:85-94.
22 2 Tiranti, K., J. Hanson, J. Deen, and B. Morrison. 2003. Description of removal patterns in a selected sample of sow herds. In: Proceedings of the Allen D. Leman Swine Conf. 30:194-198.


Table 1. Summary of reported culling parity and rate (Adapted from Stalder et al., 2004).

Table 2. Causes for mortality in breeding sows (Adapted from Stalder et al., 2004)