Maternal Line Program (MLP) data shows sows from some genetic lines will farrow nearly 50% more live pigs in their productive lifetime.

Fertility and prolificacy serve as the productivity yardsticks by which sow herd output is measured.

Seedstock suppliers have made some effort to improve prolificacy traits such as pigs born and litter weaning weights. Both traits are easily measured by suppliers and the commercial producers using their genetic lines.

However, low heritabilities for these traits and joint selection for growth and carcass traits have kept genetic improvement of prolificacy traits at a relatively slow rate.

Fertility traits, such as age to puberty and farrowing rate, have been given less attention by genetic suppliers because of the great difficulty in getting reliable data. Still, these traits greatly influence the length of time groups of gilts will remain productive in the sow herd. These groups are commonly called "cohorts."

More precisely, a cohort is defined in the National Pork Producers Council's (NPPC) Production and Financial Standards as "a group of animals that shares a common event within a defined period of time."

The advantage of cohort comparisons is it allows us to target groups of gilts as they enter the sow herd and follow them through multiple parities. This approach requires close accounting of all gilts entered into the herd. In the end, longevity is a reflection of a female's fertility traits.

Fertility vs. Prolificacy Comparisons of fertility traits depend on all records whereas many sow recordkeeping programs only account for prolificacy traits. In other words, they only track sows that mate and/or farrow.

Improving the average herd life of breeding females reduces genetic costs and gilt development costs. And, there's the added advantage that sows tend to wean heavier pigs than gilts and have acquired immunity to specific herd diseases. Therefore, sows that remain productive through more parities can increase herd output while reducing cost of production.

The NPPC Maternal Line National Genetic Evaluation Program (MLP) reported the performance of six genetic lines through four parities (see National Hog Farmer Blueprint, "Maternal Line Genetics," April 15, 2000). However, NPPC continued to measure sow performance on the MLP lines after the official test was completed. Data is now compiled and evaluated through their sixth parities.

The 3,283 gilts entering the MLP were grown in a high-health, gilt development program to 165 days of age. Gilts were then placed in two new, 1,600-sow breeding-gestation-farrowing facilities. No gilts were culled for poor growth or backfat.

Matings started when gilts reached 210 days of age and were on their second or later estrus. Gilts that were not successfully mated by 300 days of age or had failed to conceive after three mating periods were slaughtered.

Sows were given 50 days after weaning to conceive. No gilt or sow was culled due to poor litter size or low litter weight.

The 25-female cohorts shown in Table 2 are formed by line-age-facility subclass at 165 days of age, as reported previously through four parities (see National Hog Farmer Blueprint, April 15, 2000,). Large lifetime differences in cohort performance were found between genetic lines, highlighting the opportunity for improved total herd efficiency by selection of sow genetic line.

Ranges in output of the 130 cohorts show the great biological opportunity in production efficiency that is still possible. Table 3 shows the extremes in production from a 25-female cohort. The total possible litters born from a 25-female cohort over six parities now stands at 150. Actual records show a range of 40 litters for the worst cohort group to 127 litters for the best.

The most productive cohort farrowed 1,347 live pigs during its six-parity productive life while the poorest farrowed only 397.

Clearly, measuring and comparing these fertility traits are a truer measure of performance than are prolificacy traits.

Nearly 50% More Pigs The combination of superior sow longevity and superior number of live pigs born/litter gives the Dekalb GEPK347 line female a lifetime live pig born output advantage of 48% more than the average of the other five lines. (This genetic line was originally called Dekalb Monsanto MXP200.) Note that this advantage is due mostly to the superior fertility of GEPK347 gilts in their first and second parities. This line produced 36% more litters through their sixth parity.

After the first two parities, the percentage of sows leaving the herd due to illness, injury, death and infertility is nearly the same in each parity for all genetic lines.

The figures in Table 4 reinforce that an opportunity to improve sow longevity exists by developing gilts with the highest P1 farrowing rate. Simply stated, the gilt must farrow a first litter. Anything done to improve her first parity farrowing rate should indirectly improve sow longevity.

The heritabilities of fertility traits are low to medium, so improving the environment in which gilts are developed should improve farrowing rates.

Economic Considerations The number of live pigs born/day of herd life may give a clue. If preweaning mortality is 10% and the value of a weaned pig is $25, then the daily income/sow for the best line (0.068 pigs/day) is $1.53, for an average line (0.060 pigs/day) is $1.35 and for the poorest line (0.054 pigs/day) is $1.21. The difference is 26% more income from the best line versus the worst line sows.

The first opportunity for improving herd performance is selecting a maternal line with higher fertility. Of course, this is easier said than done given the lack of reliable data available. However, sow longevity may be improved by implementing gilt development programs (i.e. gilt nutrition, boar stimulation, acclimatization) to better prepare gilts for mating success.

Improvement in prolificacy traits, such as pigs weaned/litter, has been remarkable throughout the industry. The results presented here show the great opportunity that still remains for increasing breeding herd output. Greater attention to fertility traits is needed to capture this opportunity.

Producers and accounting professionals have provided new tools for breeding herd evaluation. Programs that use the new NPPC Production and Financial Standards will give producers a true picture of their breeding herd efficiency.