CategoryAnimal Science - Animal Science
Date Full Report Received07/18/2007
Date Abstract Report Received07/21/2008
Funded ByNational Pork Board
Sow productive life, also called sow longevity, in commercial operations has drawn considerable attention over the past several years. It has been noted that there are genetic differences observed between the vast commercial lines available to the commercial producer. However, the underlying genetic causes which are responsible for these differences have not been studied until now. There has been a wealth of research on lifespan in model organisms such as the mouse, fruit fly and nematodes that show associations with certain genes to simple lifespan. The common theme between several of the genes the researchers found was that most of these genes were associated with either growth or were involved in regulating caloric intake. Our working hypothesis was that the same genes that showed association with lifespan in model organisms could also be associated in some way with sow productive life. Furthermore, we fully realized that sow productive life was a complex trait that included several components in addition to lifespan such as reproductive performance, disease resistance, feet and leg structure, as well as the many management decisions that complicate the trait. Genetic markers were identified in twenty different candidate genes spread throughout the swine genome. All markers were originally tested in three uniquely different populations to identify their association with either longevity itself or reproduction traits. The first population consisted of approximately 1,000 commercial sows where half were older sows with 6 or more litters and the other half had less than 4 litters at the time of data collection. The second population consisted of 200 sires with a minimum of 10 daughters per sire. The reproduction records of the daughters were used to estimate the breeding values of the sires for longevity and reproduction traits. The third preliminary population consisted of reproduction records for 1,200 sows without any longevity information. All of these populations existed during the mid to late 1990s and reflected the genetics of that time period. Six genetic markers were dropped from the study after these initial populations were studied because either almost all of the animals tested had the same genotype or the marker showed no association with any longevity or reproductive trait. The fourteen remaining markers showed promise to being associated with longevity or reproductive traits, but needed to be validated in a commercial population with as current of genetics that a longevity study will allow.
In the fall of 2005, tissue samples were acquired for DNA isolation on a fourth population to be used to validate earlier results. This population was comprised of approximately 2,000 commercial sows across three farms with half of the sows having produced at least five litters while the remaining thousand sows were gilts ranging in age from seven months to gilts about to farrow their first litter. The sows with five or more litters were selected as a more ideal or superior sow that out produced the industry average by at least 1.6 litters. The young gilts served to represent the average gilt that enters commercial production. These females were also divided such that half of the sows were PIC C22s and the remaining were PIC L42s. PigChampTM records were available to be downloaded to obtain general reproduction information and longevity records such as the number of days in the herd and the total number of parities that each female produced.
Some sows failed to have a first record, primarily due to internal id problems. From the 943 young females with PigChampTM records, 62 (6.5%) failed to produce even a single litter. A total of 13.9% of the sows that produced 1 litter failed before they produced their second litter. A total of 15.6% females that produced 2 litters failed to produce a third litter. Finally, 15.5% females that had 3 parities failed before producing their fourth litter. There are an additional 30 sows that have yet to farrow their fourth litter though they have had enough time and probably should have been culled do to reproductive difficulties. In total, 46.1% females have either dropped out or are not producing at acceptable levels before producing a fourth litter. Additionally 81 females have dropped out after producing four parities while 10 were removed after producing 5 litters. Of the 494 young females that have been removed from the farm to date, 25 sows had to be euthanized, 63 died, and 406 were culled. This means that not only did the farm lose the opportunity to get salvage value on 88 head (9.3% of the young sows), but they also had the added expense of removal on these sows.
Of the 494 young females removed to date, 56 were removed because of feed intake/body condition, 23 had gastro-intestinal issues, 24 were removed because of heart issues, 110 were removed for leg issues, 21 were culled for multiple systems failure, 36 were culled for productivity reasons, 174 were culled for reproductive issues, and the remaining 50 sows were culled for irregular reasons. The predominant reason for removal before the first parity was reproduction (n=31). The primary reasons for removal between parity one and parity two are reproduction (n=46), feet and legs (n=25), and feed intake/body condition (n=18). Likewise, the primary removal reasons between parity two and three are reproductive issues (n=28), feet and leg issues (n=30), and feed intake/body condition (n=16). Again, between parities three and four as well as between parities four and five respectively, reproductive issues (n=38 and 28) and feet and leg issues (n=29 and 20) were the primary culprits for removal reasons while for the first time sows were remove for productivity reasons (n=15 and 12).
The sows were genotyped for all genetic markers and initially were tested to see if there existed a difference in genotypic frequency between the superior older sows and the gilts. A difference in the genotypic frequency shows evidence of the marker being involved in the sows’ ability to survive to parity 5. Seven genes showed a significant difference between the genotypic frequencies of the superior sows and the young gilts. These seven genes were insulin-like growth factor binding protein 1 (IGFBP1), insulin-like growth factor binding protein 3 (IGFBP3), carnitine O-palmitoyltransferase I (CPT1A), organic cation/carnitine transporter 2 (Solute carrier family 22 member 5; SLC22A5), angiotensin I converting enzyme (ACE), and C-C chemokine receptor 7 (CCR7), tryptophanyl tRNA synthetase 2 (mitochondrial) (WARS2). More precise measurements of sow longevity were also tested using PROC LIFETEST and PROC LIFEREG of SAS on the young sows. Markers were tested using these two procedures for both the sows’ ability to survive in days as well as surviving to certain parities. The days that we chose to analyze were surviving to 250 days after their first service, to 500 days after first service, and to June 26, 2007 (the last time the PigChampTM records were downloaded before this publication). Additionally we tested the sows’ ability of surviving to produce 1 litter, a second litter, a third litter, and a forth litter.
The PROC LIFETEST analysis showed that there was not a significant difference between the two genetic lines tested in any analysis of survival to a certain day or parity. However, there was a large and significant difference between the two farms that both contained the L42 animals. The genetic marker for CCR7 was significantly associated with survival to parity 1 and survival to 250 days as well as tending towards significance for total active days in the herd and survival to 500 days. The genetic marker CPT1A was significantly associated with surviving to parity 4 and tended towards significance for total active days in the herd. The genetic marker MBL2 also tended towards significance for survival to parity 3, parity 4, and total active days in the herd. Additionally, IGFPB1 and WARS2 were also both tending towards significance for surviving to 250 days. When the effect of farm was taken into account with PROC LIFEREG, CCR7 tended towards significance for surviving to 250 days. MBL2 tended towards significance for both survival to parity 4 and total active days in the herd. The best results came with CPT1A being significantly associated with survival to parity 4 and total active days in the herd while also showing a tendency for being associated with survival to parity 3 and surviving to 500 days in the herd.
The reproduction analysis of these genes also proved to be beneficial to understanding the different roles these genes play in sow productive life. The reproductive traits that these markers were tested for included the total born in each litter and the number born alive in each litter for parities 1 through 4 individually, the number of pigs (born alive) per day of herd life, and the cumulative number of pigs (both total born and born alive) produced over the sows’ lifetime. Additionally, these traits were analyzed using all of the sows’ reproduction records, just the superior sows’ records, as well as just the young sows’ records. The genetic marker IGFBP1 was significantly associated with several reproductive traits for the different sow groups. It was significant for the number of pigs born alive in parity 1 in the young sows with the favored genotype having 1.22 and 0.96 more pigs than the other genotypes, the total number of pigs born and the number of pigs born alive for the superior sows second litter, the total number of pigs born in parity 4 for all sows, and for the total number of live pigs over the superior sows’ lifetimes with the beneficial genotype class having 2.48 more pigs than the unfavorable genotype class. After dropping the 11 genotype class from further analysis (which represented less than ten percent of the data), MBL2 genotypes were significantly associated with differences among early reproductive traits. This genetic marker was significant for the total number of pigs born and for the number of pigs born alive in parities 1 and 2 when all sows were analyzed together with the beneficial genotype class having an additional 0.35 pigs per litter for all traits. The CPT1A genetic marker was significantly associated with several reproductive traits as well, especially in the later parities. The favored genotype class was associated with at least a 0.4 advantage in total number of pigs born and number of pigs born alive for all sows in parities 3 and 4. Additionally the same genotype class had an advantage of 0.005 more pigs per day on the farm for the young sows representing 1.8 more pigs per year per sow. VDR (missing the 11 genotype) was significantly associated with total number born in early parities and in total production for both the superior and young sow groups though identifying the favorable genotype class in not strait forward. Other markers such as SLC22A5, ACE, and CCR7 also were associated with some reproductive trait, though they were not as consistent across sow groups or parities.
In total, several genetic markers were found to be associated with traits involved in sow productive life. These included CPT1A, CCR7, IGFBP1, WARS2, and MBL2 which were all significantly associated with sow survival, either to a certain parity or day, when tested using extremely stringent analysis. The genetic markers IGFBP1, MBL2, CPT1A, CCR7, SLC22A5, and ACE all were significant with at least one reproductive trait. It should be noted that the favorable genotype for sow survival was the favorable genotype for reproductive traits for CPT1A, IGFBP1, and MBL2. However for CCR7, the favorable genotype for sow survival was the unfavorable genotype for reproductive traits. For CPT1A, IGFBP1, and MBL2, not only are these sows surviving longer, but they are simultaneously producing more pigs than their contemporaries. Though extremely positive, further research needs to be carried out on these genetic markers in other sow populations to verify the results before these markers are incorporated into selection protocols.