The U.S. pork industry continues to experience steady genetic growth. Sows today are genetically able to produce more marketable pounds in a quicker time frame than ever before, but are U.S. sows meeting their full genetic potential? Research shows that some sows may not, due to shortages in nutrition.

When adequate nutrients are not supplied to sows through their ration, they are unable to meet their optimum sow lifetime productivity — or SLP. The National Pork Board defines SLP as the total number of quality pigs weaned during the productive lifetime, from the time the gilt becomes breeding eligible until it leaves the herd. NPB indicates that SLP potential is higher than ever before as sows are genetically capable of producing 30 pigs per sow per year.

You can maximize the SLP growth trend by focusing on PSY rates as well as working to enhance the number of full-potential pigs. Recent work by PIC shows the potential to produce 30 PSY is possible with the genetics in place today. The researchers estimated the United States’ genetic potential at 26 PSY in 2004, with genetic improvements pushing that potential to 28.5 pigs in 2010 and closer to 30 PSY today.

Though most U.S. sows have the potential to produce 30 full-potential pigs annually, very few U.S. producers are reaching this production opportunity. Research shows that low PSY rates on an operation may be attributed to early exit of sows from the herd and high pre-weaning mortality rates traced back to low birthweights. Focusing on sow nutrition can help minimize both of these issues.

Early Exit of Sows from the Herd

When sows exit the herd before becoming profitable, a facility’s SLP drops significantly and its bottom line is impacted. Recent Iowa State University research shows that sows reach their breakeven point economically in the third parity and are most profitable when they remain in the herd for six to nine parities, depending on variable costs. (Go to

At this fall’s Allen D. Leman Swine Conference, Steven Pollman of Murphy Brown, Western Operations, in Ames, Iowa, presented information on sow lifetime productivity, explaining that U.S. sows exit the herd on average between parity 3.3 and 3.7 and that sow replacement rates average 50 percent to 60 percent annually. Due to early herd exit, Pollman said that many parity 1 and parity 2 sows never reach the 30 PSY goal. In fact, approximately 42 percent of all sows produce only 19 or fewer full-potential pigs in their lifetimes. But this can be improved by feeding sows for long-term productivity before their first parity.

“A 30 percent improvement (in sow retention) would result in average herd longevity of 4.6 parities and an increase of 10 to 15 pigs weaned per sow lifetime,” Pollman said. He estimated that increasing the average number of litters by one litter per sow in her lifetime would produce a net value of $250 million for the U.S. pork industry.

Pollman added that, if the developmental cost per gilt was $400, the ability to produce an extra litter would leverage the replacement gilt’s cost for an overall reduction in the weaned pig cost of $1.90 per head.

To reach this economic potential and improve sow longevity, one must first examine why sows leave the herd early. USDA’s Animal and Plant Health Inspection Service research shows that 23.7 percent of sows are culled because of poor performance, while only 11 percent exit due to old age. Primary reasons for culling include small litter size, high pre-weaning mortality, low birthweights, failure to rebreed on schedule and sow health.

Though other issues are often at play, many are heavily linked to sow nutrition. As sows begin to produce additional pigs per litter, dietary nutrients also need to be ramped up to meet increased production requirements. Calculations on the nutrients required per pig produced (or on pounds of litter weaned) indicate that an extra 200 to 300 pounds of feed is required per pig to sustain today’s production as compared to levels five years ago. To keep sows in the herd longer and to achieve 30 PSY, even more nutrients are needed.

Real results can be seen when the added nutrients are provided. For example, one Iowa herd that we work with is striving for 30 PSY in its 3,000-sow, farrow-to-finish operation. The biggest advances were seen when ad libitum feeding occurred at farrowing versus a restricted-feeding strategy. The increase in nutrients consumed allowed the herd to reduce culling rates and improve its total pigs born from 24.8 to 26 PSY. Birthweights also climbed from 2.9 to 3.2 pounds per pig, and weaning weights increased nearly half a pound per pig in the one year between the feed change. The added nutrients also played a role in enhancing overall sow health and reduced days to rebreeding.


Increasing Full-potential Pigs


The producer’s transition to a higher plane of nutrition paid dividends through the sows’ ability to produce more full-potential pigs. Birthweights are heavily impacted by sow nutrition and the nutrients provided during gestation, so the 0.3 pound increase in birthweights is likely linked to the producer’s nutritional transition in the sow facility.

A focus on birthweights is especially important as the industry moves toward larger litters. Estimates show that a pig’s average birthweight drops approximately 0.10 pound for every additional pig in the litter. However, the Iowa producer was able to increase birthweights and maximize the sows’ genetic potential for larger litters by focusing on sow nutrition through gestation and lactation.

Of course, low birthweights are especially concerning because the initial birthweight impacts not only survival rates but also the pig’s lifetime performance potential.

Retrospective studies from large datasets suggest that sows with increased gestation-feed intake typically produce pigs with higher average birthweights. For instance, a recent study of eight operations showed that sows on farms feeding approximately 100 pounds more feed per year in gestation produced piglets that were 0.47 pounds heavier on average than piglets from sows receiving less feed. Researchers indicate the only management differences between the high- and low-birthweight farms were those related to sow feed allowance during gestation and in feed quantity during the weaning-to-breeding interval.

To test the theory that sows fed additional nutrients are better able to perform, researchers at Purina Animal Nutrition Center in Gray Summit, Mo., have monitored sows through several parities and analyzed progeny performance. An ongoing study shows that sows fed to a higher nutritional plane are better able to produce heavier-born pigs. In addition to increased sow health, the 1-pound difference in birthweight (3.1 pounds versus 2.1 pounds) can result in twice the pre-weaning survival rate.

What’s more, the benefits continue through the production cycle, including growth rate and feed efficiency improvements. After five years and 2,456 litters, the research shows that pigs with initial birthweights of 3.1 pounds weighed 3 pounds more at weaning than those with birthweights of 2.1 pounds. The heavier pigs also reached market weight seven days sooner than the lighter-born pigs.

These improvements can pay significant dividends when tallied together over time. A look at our Swine Profitability Economic Model shows that a pig with an ideal birthweight of 3.1 pounds could bring an additional $1.39 at weaning or $2.72 additional profit at finishing than a pig born weighing 2.1 pounds.

As illustrated through numerous studies, the first step in reaching ideal benchmarks for birthweight, pig performance and sow longevity is to increase nutrition levels in gestation and through lactation. Indeed, the ration fed to a sow through all stages of production can impact the performance of her progeny and her long-term profitability, which will help the entire herd meet its full genetic potential.