Sow longevity is a problem for the entire pork industry, but it’s more of a problem for some producers than others. Differences in sow longevity between producers can be seen in the industry’s variation in replacement rates.

“Replacement rates range from 35 percent to 65 percent across different production systems,” says Noel Williams, technical operations director for PIC. “Since replacement rates are 95 percent a function of sow longevity that shows the variability in sow longevity.”

With some sows achieving eight parities and others not making it to three, the difference can put a big dent in your herd’s productivity and profitability. It’s well known that gilts aren’t as productive as older sows, so the fewer gilts you have at any given time, the more productive your herd is likely to be.

To determine what, if any, changes you need to make, evaluate where you are on the sow longevity curve. PigChamp keeps producer data, including the mean, upper 10 percentile and lower 10 percentile. (See sidebar.) Williams says a replacement rate of 45 percent is a realistic goal.

The big question then is what are the top producers doing right and how can you become one of those top producers?

The biggest factor appears to be gilt development. The first step is selecting the right gilts to enter your breeding herd. Then a thorough isolation and acclimatization program to maintain the herd’s health status is critical, as well as establishing proper feeding and management programs to meet specific genetics’  needs.

“Producers with the best sow longevity rates do a better job of evaluating gilts,” says Ken Stalder, Iowa State University swine specialist. That challenge can be compounded if producers are not skilled in selection criteria and use internal multiplication programs to produce breeding-herd replacements. There’s also the issue of stockmanship skills within the unit.”

Gilt selection takes more than a keen eye, however. It also requires discipline and a proper sized multiplication herd, and most producers don’t have enough of a cushion to accommodate their breeding targets.

“A lot of producers set selection rates too high, and allow marginal animals into the breeding herd. They breed gilts that are too young or that don’t weigh enough,” says Williams.

This causes herds with poor sow longevity to continue to get worse, which then causes them to introduce even more marginal animals. Williams refers to this as the “death spiral.”

He says the number of multiplication sows in a herd should be about 12 percent of the number of “commercial” sows currently in the breeding herd. This gives you some insurance, in case they don’t all pan out. So, if you have 10,000 commercial sows you should have 1,200 sows in the multiplication herd.

But management that emphasizes sow longevity only begins with gilt selection. Stalder says you need to consider every aspect of your system and how it all interacts.

“You need to have the right genetics for your environment,” says Stalder. “The temperaments and heartiness of some sows or gilts might fit better with either pen or crate gestation. For example, some ultra-lean genetic lines may not have the body reserves to survive in a pen gestation environment.”

Even though genetics are a big piece of the puzzle, sow longevity has not been a significant component of animal-selection indexes in the past. Production traits and carcass leanness have been the priorities, but sow longevity is gaining momentum.

“PIC has been selecting for sow longevity for several years, but has increased the ability to accurately measure longevity in the last two to three years,” says Williams. “We are now able to measure more animals more accurately at the commercial level.”

Sow longevity is gaining momentum as a selection criteria with other genetic suppliers as well.

Barbara Straw, DVM, Michigan State University says the focus on selecting for extreme productivity has had physiological effects on breeding females, which have negatively impacted sow longevity.

“In the 1990s through about 2002, everyone just focused on producing high numbers of ultra-lean animals,” says Stalder. “When we started seeing breeding-herd mortality reaching more than 10 percent, the industry started to take notice.”

Stalder says changing genetics will take time to see results.  Gilt selection may have quicker results than genetic selection, but also will raise replacement costs he notes.

“Putting better quality gilts in the herd, and breeding them at the correct age and weight will probably pay the quickest dividends,” says Williams. “It will take six months to a year to see much improvement.”

Once the momentum shifts, however, you should see noticeable gains for several years.

“For each farm, you need to determine specifically where your losses are occurring,” says Straw. “If you have trouble re-breeding gilts or with lameness issues you need to examine your breeding programs,  facilities and environment.”

All of these things combine to affect sow longevity, with no one easy answer. Breeding failures and lameness are the top two causes for culling sows, but many factors affect lameness and breeding.

Stalder says inadequate heat detection is a major factor in sows and gilts not getting bred, and he says recordkeeping is the key to solving the problem.

“You need to identify when breeding problems occur,” says Stalder. “Find the common denominator, then work to solve the problem.”

Records let you track which AI technician bred the animal, which boar provided the semen and which day, week or month the problems occurred. This can tell you if there is an employee problem, a semen-quality issue, problems with bacteria and whether AI equipment needs to be cleaned.

Another thing to keep in mind is that old sows are not necessarily better — eventually there are diminishing returns. Straw says that older sows remain more productive than gilts up until their sixth litter, after that they usually become less efficient, though there are exceptions.

“A gilt litter is about one-half to one pig smaller than a sow litter,” says Straw. “A sow’s third litter is about another one-half pig larger than its second litter. Sows then plateau until after their sixth litter.”

The older sows’ fall-off illustrates that there are no absolutes when it comes to sow longevity. It takes constant attention to details, an acute knowledge of where you are and a willingness to make necessary changes to climb to the top of the sow longevity curve. 

Gilt Development Cheat Sheet

Developing gilts properly is a critical component of sow longevity, but it can be tricky. Here are some points to help you remember gilt development milestones.

  • Boar exposure: Start when gilts are 150 to 170 days of age and continue as the breeding process begins.
  • Age at breeding: Gilts should be about 210 days old.
  • Weight at breeding: Gilts should weigh 280 lbs. or more.
  • Backfat: A gilt should have 17 mm to 21 mm.
  • Soundness: Foot and leg soundness is vital. Legs should have no lesions, and they should not be positioned straight up and down. For more details see the February 2005 issue of Pork.