Trends in Sow Longevity and Sow Death Rate in the U.S. Industry


Dr. John Mabry

Iowa Pork Industry Center

Iowa State University

Ames, IA 50011




The commodity pork production sector in the United States, as well as other parts of the world, has seen erosion of the average profit per pig in recent history.  This narrowing of the average profit margin has required the production sector to do everything in their capability to reduce the cost of production.  As a result the industry has pursued maternal genetics with maximum litter size born alive, as well as with minimum backfat, maximum percent lean and maximum growth rate.  From a management standpoint, the producers have embraced early weaning production systems in order to get the most litters per sow per year from each sow in inventory.  From a housing standpoint, the industry has moved to inside crated gestation housing systems to better control the environment of the sow while minimizing the labor costs.  As the industry has moved to these extremes in both performance and management and housing there exists the possibility for these more extreme animals to be less fit in terms of disease resistance, livability and longevity. 


As swine seedstock suppliers have selected for more extreme leanness, there has been reported a corresponding decrease in sow longevity.  Brisbane and Chesnais (1996) defined sow longevity as the lifetime number of litters produced by a sow.  They reported that “there is in fact a strong association between leaness and sow longevity.  It would appear that the lean sows do not remain in the herd for as many parities”.  These conclusions were based on an analysis of purebred Yorkshire and Landrace sow records in the Canadian national purebred swine database.  Stalder et al (2001) examined a similar trait using records of growth, composition and reproduction from the National Swine Registry purebred database of Landrace females.  They found that backfat group was a significant source of variation for lifetime number of pigs born alive and maximum number of parities.  They stated that “gilts having more backfat will have more live born pigs during their lifetime as breeding females.  The basic reason for this is that they are retained in the breeding herd for a greater number of parities”.


The purpose of this paper is to investigate the phenotypic trend in sow longevity in independent producer commercial herds of swine over the past ten years.


Methods and Materials:


Commercial swine producers who agreed to cooperate with researchers at the Iowa Pork Industry Center provided the datasets used for this analysis.  There were 42 cooperating herds that provided data for this analysis.  The data provided was in the form of PigChamp® reproductive data management files.  The size of the sow herds providing this data ranged from 110 sows to 2500 sows in annual average sow inventory.  The data analyzed were records of sows removed from 1992 through 2002. Reproductive data was extracted from the PigChamp® datasets using the Database Applications subroutine within the Breeding Herd Reports section of the software.  The output variables for each sow in each herd included removal date, sow ID, removal parity, removal reason, sow genetics and farm ID.  Purebred sows were excluded from the data analysis.  The total data set size analyzed was 142,494 removed sows.  The commercial swine herds that provided data for this analysis all used seedstock suppliers that were part of the National Swine Registry purebred national nucleus in the U.S.  None of the herds used in this analysis utilized genetics provided by the major seedstock companies in the U.S. 


Sow longevity was defined as lifetime number of litters produced by a sow in her lifetime (Removal Parity), similar to the definition used by Brisbane and Chesnais (1996).  Data were analyzed using the GLM procedure of SAS with the fixed effects of farm and removal year.  Other effects such as sow genetics could not be fit, as they were not consistently represented across all herds and years.


Results and Discussion:


Least squares means for removal parity by removal year are shown in Figure 1.

The means for average sow removal parity by removal year are consistently in the range of 3.4 to 3.6 except for the years of 2000 and 2001.  These results would not support the conclusion that sow longevity, as defined by average sow removal parity, has decreased over the past ten years in the herds used for this analysis.  The reasons for the increased sow removal parity in the years 2000 and 2001 may be due to economic hardships from 1998 and 1999. 


Average sow inventory numbers have increased from 362 sows/herd in 1992 to 729 sows/herd in 2001 and have dropped to 656 sows/herd in 2002.  The relationship between average herd size and sow death rates are shown in Figure 2.


These herds have shown a steady increase in average sow inventory from 1992 until 2001, then a decrease in 2002.  The average annual sow death rate was somewhat steady between 4 to 5 percent from 1992 until 1998, then has increased to approximately 6 percent from 1999 to the present.  These sow mortality percentage changes and herd size changes are in agreement with results reported by Loula (2000). 


A breakdown of the reasons for the sows being removed from the herd is shown in the following table:


Removal Reason


Reproductive problems


Physical problems




Milking problems


Management decision


Poor performance





Reproductive problems included such events as abortions, did not conceive, difficult pregnancy, failure to farrow, found in heat, heat no service, no cycle, rebreed, tested open.  Physical problems included such events as bad udder, behavior, body condition, downer, injury, lameness, prolapse, size, spraddle, unsoundness and unthriftiness.  These results are in agreement with those presented by Paterson (1996).




Trends in sow longevity, defined as average parity at removal from the herd, and sow death rate were examined in data sets provided by 42 swine herds in the U.S.  The data used for this analysis was from sows removed from the herd and sows that died from 1992 to 2002.  The genetic suppliers to these sow herds were independent purebred producer members of the National Swine Registry.  Average sow removal parity remained somewhat constant from 1992 through 1999 at between 3.4 and 3.6.  This average removal parity increased to 4.0 in the years 2000 and 2001 before declining to 3.4 for 2002.  The average sow mortality percentage was somewhat steady between 4 to 5 percent from 1992 through 1998 and increased to a level above 6 percent after that.  The primary reasons for sow removal were reproductive problems and physical problems.




Brisbane, J.R. and J.P. Chesnais. 1996. Relationship between backfat and sow longevity in Canadian Yorkshire and Landrace pigs.  Proc. 1996 NSIF Annual Meeting,


Loula, T. 2000. Increasing sow longevity: the role of people and management.  Bacon Bits Vol. IX, No. 10, October 2000.


Paterson, R. 1996. Approaches to increasing sow productive lifetime. South African Research and Development Institute, http://


Stalder, K.J, A.M. Saxton and G.E. Conatser. 2001. Growth and compositional effects on sow productivity traits in purebred Landrace swine.  In: Department of Animal Science Report, University of Tennessee Animal Science Department, Knoxville, TN 37996.