Modern replacement gilts have a greater genetic potential for lean growth and cost more to purchase or multiply internally. Consequently, producers want large litters of heavier pigs at weaning, sows that recycle quickly, conceive consistently and farrow and wean large, successive litters.

Some producers manage sows in controlled facilities, while others prefer loose housing or pasture systems. All want top performance.

Industry benchmarks for breeding herd productivity and lean growth rates keep rising. These demands are taxing. Unfortunately, the rate at which sows fall out of the breeding herd, whether from death, illness, injury or reproductive failure, tends to creep higher as pressure on performance parameters intensifies.

It is widely accepted that older sows farrow larger pigs and have a more developed immune status than gilts. And, it is generally true that reproductive performance increases until third or fourth parity and may be maintained until sixth parity.

The bottom line is clear — sow longevity increases a producer's economic return.

Clues to Sow Survival Rates

There are many theories about how to build long-lived sows. Most are over-simplified. The heritabilty of sow performance and longevity traits within breeds or lines is estimated at 5-20%. Genetic breed or line differences can be very large, depending on the environment and management sows are exposed to. Some sows thrive in a pasture management system while others give their best performance in a controlled environment system. A breed or line may not have the genetic potential to succeed in all types of systems.

Therefore, the challenge is to predict which sows will survive, which will not. Another look at the checkoff-funded Maternal Line National Genetic Evaluation Program (MLP) results provides some clues.

Genetic lines represented were American Diamond Swine Genetics, Danbred USA, Dekalb Choice Genetics (two lines), National Swine Registry (Yorkshire x Landrace F1) and Newsham Hybrids.

Roughly 3,600 gilts (600 per line), 10-20 days old, were grown in wean-finish barns. At about 165 days of age, 3,283 gilts were moved to two new, 1,600-sow, breed-to-wean facilities. Gilts were checked for heat (estrus) daily and serviced on their second or later heat period. All matings were done by artificial insemination using fresh semen from one unrelated sire line.

The MLP goal was to evaluate the six genetic lines through four parities. An important design requirement was that no gilt or sow could be culled simply for poor reproductive performance (i.e. small litters, poor milking ability, etc). The only way that a female could leave the program was death, injury or failure to conceive within 50 days of weaning.

The amount of daily gestation feed given each sow was determined by her weight and desired weight gain before farrowing. All sows were fed three times daily during lactation to maximize feed intake. Daily lactation feed disappearance for each sow was recorded. Average weaning age was 15.4 days.

Genetic Line Differences

The sow loss rate of the Dekalb GPK347 line was different from the other five lines; therefore, it is listed separately, while the other five lines were pooled (see Table 1). The GPK 347 line, originally called Dekalb-Monsanto MXP200, was derived from a cross of the company's DK44 line with a University of Nebraska experimental line that was selected for increased ovulation rate, embryonic survival and litter size at birth for 16 generations.

Table 1 shows that the greatest barriers to sow longevity are gilt and post-first parity sow loss due to reproductive failure up to 450 days of age.

Gilts that are never serviced or fail to conceive by 330 days of age show the difference between the GPK347 and other lines. Many producers fail to account for the cost of feed and facilities for these infertile gilts. The National Pork Producers Council (NPPC) Financial and Production Standards require entering all gilts into the sow herd when delivered or selected. Litters and/or pigs per sow year ratios will be reduced to their true value when the NPPC Standards are used.

Similarly, failure to rebreed is the major component of sow loss between 331-450 days of age, which basically reflects first parity sow fallout.

MLP records were grouped according to how long a sow remained in the herd (longevity or “L” group) and then further divided into parity groups. Only sows of the five lines that farrowed at least one litter are included in Table 2. The Dekalb GPK347 females had different performance indicators for many traits and are not included in Table 2.

The first four columns show the performance of Parity 1 females.

The first column shows Parity 1 performance of females that were lost from the herd after their first parity (P1-L1). The second column then shows Parity 1 performance of females that were lost after two parities (P1-L2). The other columns follow this pattern until the last column shows the Parity 4 performance of females that completed the MLP with four parities (P4-L4). This table allows us to search for performance indicators at the end of each parity that might predict sow loss.

Longevity Indicators

Age at first estrus — Table 2 shows the gilts that showed heat younger stayed in the herd longer. Sows that finished four parities (P1-L4) were a week younger than other sows when showing first heat. The GPK347 gilts were 12 days younger than the other lines.

Age at first farrowing — The P1-L4 sows were 10 to 13 days younger when they farrowed their first litter. The GPK347 gilts were 12-17 days younger at first farrowing.

Sow weight — All gilts were fed about 5 lb. of feed daily during gestation. The sow weight at first parity shows the longer-lived sows were actually slightly smaller at first parity. Sows that were lost after first parity (P1-L1) had the greatest lactation body weight loss, 63 lb.

The individual sow gestation feeding program was designed to maximize the growth and reproductive performance of each sow. All sows grew larger as they got older.

Sow backfat thickness (last rib) — Backfat depth was not different for any herd longevity group. Sows had their greatest backfat thickness at first parity farrowing. The lactation backfat loss for each herd longevity group was also the same within each parity. Even though the sows grew heavier during each gestation period, they were never able to achieve the body composition they had going into their first parity.

Total pigs born and number of pigs born alive were different only for the Parity 1 herd longevity groups. The sows that weaned four litters (P1-L4) had more P1 pigs and live pigs born than the other three longevity groups.

Each female was given an equal chance to raise a litter. Within 24 hours of farrowing, all litters were crossfostered to about 10 pigs/sow. The number nursed reflects this practice.

Number of pigs weaned and litter weaning weights are not different for the herd longevity groups.

Lactation feed intake — First week lactation feed disappearance records (Day 1-7) show at least 1 lb. lower feed intake per day by the Parity 1 sows that were lost before Parity 2 (P1-L1). Day 8 to 14 lactation feed records also show a lower feed intake for P1-L1 sows. These P1-L1 sows were weaning just as many pigs as the other Parity 1 sows.


It is very difficult to predict sow longevity from performance data because there are very few real differences among groups shown in Table 2. The strongest signals are age at first farrowing, lactation feed disappearance and sow weight loss during lactation. Problems in those areas could prevent a sow from expressing post-weaning estrus, resulting in her being culled for reproductive failure.

The Dekalb GPK347 line females confound some of the observations just made from the other five lines' performance. These females are smaller, lose more weight during lactation, and eat less feed during lactation, yet farrow more pigs and breed back more often after weaning. About 70% of GPK347 line females survived through four parities versus 50% of the other five lines. Nearly all of the longevity difference was due to fertility differences prior to 450 days of age.

For more information or MLP results see National Hog Farmer Blueprint: “Maternal Line Genetics,” April 15, 2000 or contact National Pork Board at (515) 223-2600 to request complete results.

Table 1. Maternal Line Program Sow Loss Rates by Age of Breeding Females

Genetic Line *150-330 days old, % 331-450 days old, % 451-570 days old, % 571-690 days old, % 691-810 days old, % **Sold after Parity 4, %
Average of 5 lines 18 11.7 8 6.4 5.3 50.6
Dekalb GPK347 6.1 8.8 4.9 5.7 4.6 69.9
*Includes culling of gilts not expressing estrus by 310 days of age.
**All sows were sold after weaning their fourth parity litter.

Table 2. Litter Parity by Herd Longevity Group Performance in the Maternal Line Program (average of five lines)

Parity by Life P1-L1 P1-L2 P1-L3 P1-L4 P2-L2 P2-L3 P2-L4 P3-L3 P3-L4 P4-L4
Sows* 318 203 261 1042 187 257 1029 243 1032 994
Age at 1st heat, days 228 227 226 220
Age at 1st farrow, days 376 378 378 365
Sow wt., lb. 466 469 458 452 510 509 503 517 518 524
Wt. loss, lb. 63 54 53 55 46 49 51 42 39 44
Backfat, in. .85 .86 .82 .84 .81 .77 .78 .71 .75 .70
Backfat loss, in. .09 .09 .08 .08 .06 .06 .04 .05 .05 .02
Pigs born 10.4 10.4 10.4 11.1 10.0 10.9 10.6 10.8 11.3 10.9
Pigs born alive 9.4 9.6 9.6 10.2 9.2 9.9 9.8 9.6 10.3 9.8
Pigs nursed 10.1 10.2 10.0 10.2 9.9 10.2 10.0 9.9 10.4 10.0
Pigs weaned 9.2 9.1 9.1 9.2 9.0 9.2 9.2 9.1 9.3 9.1
Weaned wt., lb. 105 110 111 108 113 117 121 110 114 112
Day 1-7 lactation feed, lb 45 54 55 53 69 76 73 82 84 85
Day 8-14 lactation feed, lb. 76 82 85 82 91 99 96 105 112 109
*Number of sows with complete 14-day daily feed intake records. The number of sows with complete daily lactation feed disappearance records is slightly different within herd longevity groups due to occasional missing records.