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25 Years of Genetic Selection, Swine Nutrition Compared Structural correctness in commercial hogs is an ongoing challenge facing pork producers

25 Years of Genetic Selection, Swine Nutrition Compared

Structural correctness in commercial hogs is an ongoing challenge facing pork producers. Researchers at North Carolina State University assessed how genetic improvement and changes in nutrition programs have impacted leg structure and mobility over the past 25 years.

Pigs representative of the current commercial swine industry were compared to commercial pigs from 25 years ago. In all, 185 pigs were involved in this project.

The 1980 genetic line was produced from dams selected to minimize genetic improvement and inseminated with frozen semen from boars available in 1980. Pigs within sex, farrowing group and genetic line were randomly assigned to a feeding program.

The 2005 feeding program included seven phases where lysine ranged from 1.51 to 0.73% and metabolizable energy ranged from 3,428 to 3,651 Kcal/kg. Diets were pelleted, contained added fat and were based on present-day formulations.

The 1980 feeding program consisted of four meal diets where lysine ranged from 1.05 to 0.62% and metabolizable energy ranged from 3,262 to 3,317 Kcal/kg. These diets were based on formulations from the 1978 Pork Industry Handbook.

Three evaluators scored structural correctness and mobility based on the Pocket Guide for the Evaluation of Structural, Feet, Leg and Reproductive Soundness in Replacement Gilts.

Front and rear legs were scored on a 5-point scale: 1 = excessive set to the joints, 3 = ideal, and 5 = extreme straightness in the joints.

Front and rear view structure was scored from 1 to 3: 1 = toes out, 2 = ideal, and 3 = toes in.

Mobility scores were scored from 1 to 5: 1 = severely impaired due to injury, 3 = ideal, and 5 = severely impaired due to structure.

A genetic line-by-sex interaction was observed where 1980 gilts were straightest in their front leg joints. Pigs from the 2005 genetic line displayed more relaxed front leg joints than the 1980 pigs (scored 3.14 vs. 3.36).

A sex-by-feeding program interaction showed barrows on the 1980 feeding program were more turned in at the hock than pigs fed the 2005 feeding program.

Pigs from the 1980 genetic line had straighter rear leg joints than 2005 genetic line pigs (scored 3.47 vs. 3.31).

Based on a genetic line-by-feeding program interaction, 2005 genetic line pigs on the 1980 feeding program were the most mobile, while 1980 genetic line pigs did not differ in mobility between feeding programs.

Pigs from the 2005 genetic line were more mobile than 1980 genetic line pigs (scored 3.46 vs. 3.70).

Pigs on the 1980 feeding program were more mobile than pigs on the 2005 feeding program (scored 3.54 vs. 3.62).

“The most important impact documented in this research is that with selection emphasis placed on lean, improvements in leg structure and mobility have occurred,” explains M. Todd See, North Carolina State University Extension swine specialist. “However, changes in nutrition to improve growth appear to have hampered overall mobility.”

Researchers: J. Fix, D. Hanson, E. van Heugten, K. Lovercamp, J. Cassady and M. Todd See, North Carolina State University. Contact See by phone (919) 515-8797, fax (919) 515-6316 or e-mail:

A Closer Look at Why Sows are Culled

The intent of this study was to investigate the various reasons sows were culled from the breeding herd and to clarify the frequency, range and severity of the problems contributing to the decision to cull a sow.

Traditional sow culling studies are based on retrospective farm data, which are easy and economical to obtain. Producers typically record one reason for culling a sow without reporting the co-factors that may have contributed to the decision. These reasons are typically based on external indicators and do not incorporate evidence often revealed with internal investigation or diagnostic testing.

Researchers assessed the physical and reproductive condition of 3,158 cull sows delivered to two sow harvest plants in the Midwest. Body condition, feet, shoulders, teeth, lungs, and reproductive tracts were visually evaluated for gross lesions and abnormal conditions.

The prevalence of foot lesions was substantially higher than has been reported in other studies. The most common foot lesions observed among cull sows were rear (67.5%) and front heel lesions (32.9%). Cracked hooves were found on the front feet of 22.6% of sows and the rear feet of 18.1% of sows. Rear toe overgrowth was observed in 21.1% of sows.

Multiple lesions were associated with body condition score (BCS). Whether the lesions caused BCS to change, BCS caused the lesions, or the lesions and BCS changed simultaneously, is unknown.

The most frequently observed shoulder lesions in the study were abrasions, found on 12.5% of sows. As BCS decreased, the presence of shoulder abrasions increased.

The incidence of reproductive lesions detected in this study was substantially lower than the percentage of sows reportedly culled for reproductive failure in previous studies, and by recordkeeping summaries in the swine industry. The most common reproductive gross lesion observed were ovaries that appeared to be acyclic (non-cycling) in 9% of sows. The presence of grossly acyclic ovaries increased as body condition score (BCS) decreased.

Grossly cystic ovaries were found in 6.3% of sows, which increased as BCS increased.

Pneumonia, at 9.7%, was the most frequent systemic lesion observed in sows. The presence of pneumonia increased as BCS decreased.

Sow body condition was clearly associated with several abnormal conditions of sows in this study. Causative relationships were not established. Additional research or observations by producers may help relate on-farm culling practices to one or more lesions that had a high occurrence. Modifications of the culling protocol could then help reduce the impact of the lesion on the productivity of the enterprise.

The National Pork Board funded this project.

Researchers: Ken J. Stalder; Mark Knauer; Locke Karriker, DVM; Tom J. Baas; Colin Johnson; Timo Serenius; L. Layman; John W. Mabry; and Jim D. McKean, DVM, Iowa State University. Contact Stalder by phone (515) 294-4683, fax (515) 294-5698 or e-mail:

Sow Longevity Marker Genes Confirmed

Sow longevity has become a very hot topic as the involuntary culling of sows due to death, lameness, health or reproductive failure has been on an upward trend in U.S. swine operations.

A sow's longevity — more precisely referred to as sow productive life (SPL) — is very critical to the financial success of a swine operation. Increasing sow average parity in a herd by just one-tenth will increase profits of a far-row-to-finish operation by 23¢/market hog sold.

If this one-tenth parity improvement could be spread across all U.S. sow herds, net profit would improve by $15 million annually.

Recognizing that no studies have focused on the genes controlling SPL, Iowa State University researchers turned to model organisms such as the mouse, nematode and yeast, which have identified genes and gene pathways that are involved in the longevity of those species. Similar results hold true in human longevity studies.

Comparative genomics and candidate genes were used to isolate genes affecting both the number of productive parities a sow has and the number of pigs she produces during her productive life.

Researchers tested three sow populations for this association of the genetic markers with SPL:

  • The first data set (P1) was comprised of about 200 sires that had complete production records on at least 10 daughters.

  • The second population (P2) contained 1,100 females with complete reproduction information.

  • In the fall of 2005, tissue samples were acquired on a third population (P3) consisting of 2,000 commercial females from three farms within a 120,000-sow production system. Half the population was gilts and half were sows that had produced at least five parities, which were considered the “ideal” females. Two different genetic lines were represented. PigChamp reproduction and culling records were acquired in June 2006.

Genetic markers were developed for the genes 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) and cyclooxygenase-2 (COX2).

The genetic markers were tested for association with the sows' abilities to survive to Parity 5, the number of pigs born alive, stillborn pigs and the number of mummies.

Genetic markers were screened in P1 and P2 with only those showing a tendency for association with a component of SPL being validated in P3. The gene marker for IGFBP1, IGFBP3, SLC22A5 and CPT1A were all significantly associated with sows remaining in the herd until five parities.

Additionally, for IGFBP1, the same genotype favored for greater SPL, showed a tendency for an increase in the number of pigs born alive throughout a sow's productive life. Therefore, a sow with the beneficial genotype for IGFBP1 will not only have a greater probability of staying in the herd until Parity 5, but will also produce an additional 1.5 pigs while doing so.

SLC22A5 was associated with the number of mummies during the sow's lifetime. CPT1A was significantly associated with the number of pigs born alive in Parity 3 and higher, with an increase of up to 0.7 live pigs/litter. These results are evidence that there are genes causing variation in sow productive life and give promise to the use of marker-assisted selection to improve sow productive life.

Researchers: B.E. Mote, Ken Stalder and Max F. Rothschild, Iowa State University. Contact Rothschild by phone (515) 294-6202, fax (515) 294-2401 or e-mail: