Parity segregation first surfaced nearly 15 years ago in Canada, with a focus on improving gilt development and retention in the sow herd.

Today, the system is attracting attention for another reason — its ability to help stabilize disease outbreaks within the sow herd — most notably porcine reproductive and respiratory syndrome.

Both benefits stem from parity segregation’s hallmark, which is to establish development criteria for gilts headed into the breeding herd. It offers a more focused opportunity to meet the gilt’s unique growth requirements by providing specialized rations, early exposure to the herd’s disease status and smaller, more even social groups.

The end goal is a productive female that remains in the herd.

“Through proper management of the developing gilt we move up her parity (longevity) in the herd by at least one — from 3.5 to 4.5,” notes Camille Moore, a Quebec veterinarian who initiated parity segregation. “One additional parity translates into 9.5 more piglets per breeding female.” (See accompanying article for additional information on steps to reduce attrition rates in your breeding herd.)

Maintaining the gilt pool
Producers often initiate parity segregation to help them maintain a healthy, consistent supply of gilts based on their herd size and to be less dependent on the availability of gilts from a genetic source or supplier.

In the strictest sense, parity segregation involves a separate building site and dedicated employees. While the per-pig costs to establish a parity-segregation system would be no different than for any other facility, transportation costs would be higher, says Moore. The employee rate may also be a bit higher as “better” (and higher paid) employees are often assigned to the segregated-gilt area.

However, “by separating Parity-1 (P1) females from the rest of the herd you have the opportunity to contain disease outbreaks on both sides of the breeding-herd equation,” points out John Carr, DVM, IowaStateUniversity. “If the gilt or sow herd experiences a disease break, you can hold gilts until things stabilize without jeopardizing the entire herd’s breeding schedule and health status.”

Producers facing shortages in breeding or farrowing numbers because of disease or attrition rates are susceptible to prematurely adding developing gilts into the breeding herd in order to maintain numbers and fill crates.

“Perhaps the biggest challenge in a parity-segregation system is to never break the golden rule of adding a gilt to a P2+ herd,” says Ken Stalder, associate animal science professor at IowaStateUniversity. “Once you do, you destabilize the herd. Then it becomes a wicked cycle of needing more and more gilts due to poor conception rates or abortions due to disease.”

The gilt housing should be designed to provide some flexibility, says Carr. For example, if a disease surfaces in the gilt pool, it must be contained there. Therefore, the parity-segregated area must be able to house pregnant P1 gilts even if it requires temporary outdoor housing.

Disease stabilization
Of course, paying strict attention to biosecurity and transportation procedures is critical to protecting both the segregated and the main herds.

Adding bred P2 gilts (that had been segregated previously) to the sow herd helps reduce disease flare-ups.

“P2 females developed in a parity-segregation system have been exposed to herd pathogens at an early age (130 days), and they’ve had time to stabilize their own health status before adding them to the established herd,” stresses Moore.

PRRS and Mycoplasma pneumonia continuously circulate within a sow herd. In a disease-stable herd, this occurs at a sub-clinical level without obvious disease outbreaks. Introducing disease-naïve gilts into the herd gives the virus a chance to replicate and modify — often triggering a new disease cycle within the herd.

By incorporating a parity-segregation strategy in the sow herd “we are able to produce pigs with solid immune systems from P2 and higher sows that are stable enough for Mycoplasma that we no longer need to vaccinate,” says Moore.

According to Moore, slaughter checks have shown a three-fold reduction in the severity of lesions in P2+ progeny (12 percent), compared to P1 progeny (35 percent), despite the fact that P1 progeny are vaccinated.

Stalder recommends that parity segregation’s potential benefits be examined on a farm-by-farm basis. “Without major disease issues or high nursery or finisher mortality rates, there may be little benefit gained from moving into a parity-segregation system,” he says. “Additional facilities, labor and transportation costs need to be weighed against the costs of diseases outbreaks, lightweight pigs and cull levels.”

On to the next level
Following breeding, gestation and farrowing as a group, P1 females are placed on a controlled rebreeding system. The bred P2 females are moved into the sow herd about 30 days into their pregnancies.

But parity segregation benefits don’t end with the sow herd. By keeping P1 offspring segregated from P2+ litters from weaning through their finishing phase, you can reap additional benefits.

Pigs weaned from P1 gilts tend to be as much 1 pound lighter than pigs from older sows, and they grow nearly 5 percent slower. P1 piglets also face more health challenges. But by using a vaccination program designed for your herd and timed to the immature immune systems that piglets receive from P1 gilts, these litters finish out more evenly with fewer culls and lightweight pigs.

John Deen, DVM, at the University of Minnesota, has found that high-mortality nurseries (greater than 6 percent) on average contained 37 percent “gilt litters,” with 14 percent of the pigs weighing less than 8 pounds at weaning and 11 percent were younger than 15 old.

“Yet not all the mortality was occurring in the gilt litters,” notes Deen. “Rather, it appears that the presence of higher risk animals affects the entire population and causes higher mortality in the low-risk animals.”

In Moore’s research he found that the cost of not segregating P1 offspring from other litters adds five days to the finish time for the entire herd, along with raising disease issues.

“Producers need to look at their records and assess their mortality rates, health status and percentage of lightweight pigs during the nursery and grow/finish stages,” says Stalder. “There may be a hidden advantage to keeping P1 offspring segregated in terms of reduced pathogen exposure in the nursery and finishing stages, which translates into increased performance for all finishing pigs.”

While it may have surfaced 15 years ago, parity segregation is still presenting new opportunities and benefits. As with any technology, the challenge is determining whether or how it can work in your herd. 

Thinking Through the Basics
Some experts argue that producers need at least 2,000 sows to justify the separate facilities needed for a true parity-segregation system. While Camille Moore, a Quebec-based swine veterinarian, estimates the critical mass for such a system is 2,500 sows, he argues that the gilt-development principles apply to any size swineherd.

“Specific feeding, disease exposure and handling of gilts from 100 days of age to mating for their second parity is a must to achieve good results,” Moore stresses. “It doesn’t matter if it’s a 100-sow unit or a 25,000-sow system, we need to find a way to apply this technology.”

John Carr, DVM, IowaStateUniversity, successfully initiated a parity-segregation program where three, 1,000-sow units share in a single gilt-development program. It is set apart from their individual farms.

“It started out as a way to improve pig flow through a consistent gilt supply, but it also has served to stabilize PRRS within the three herds,” he notes. “Gilt production in the parity-segregation system could be a tool used by a number of cooperating family farms.”

While separate production facilities for gilt development and Parity-1 (P1) females are the hallmark of parity segregation it doesn’t have to mean new facility construction. The system can be achieved by sharing facilities between farms or by purchasing existing units.

Moore says that several small units are starting to use parity-segregation principles deeper into the herd — keeping P1 progeny separate from the rest.

“We don’t yet have data on the success of these efforts, but the producers recognize the importance of health and development of the P1 gilt and her offspring,” says Moore.

Here are some parity segregation considerations: 

  • Improves gilt growth and development through specialized rations targeted for the young gilt.
  • Better conception rates at first breeding and when rebreeding as P2 animals. Moore reports conception rates of 88 percent at first mating for segregated P1 gilts and 93 percent at first rebreeding for those females in the second parity. The culling rate after the first parity is 18 percent.
  • Early acclimatization of gilts (at 130 days old) to diseases present in the sow herd.
  • Stabilization of porcine respiratory and reproductive syndrome and Mycoplasma pneumonia in the sow herd.
  • Individualized rations and amounts during P1 lactation to offset the normal gilt’s weight loss of 15 percent to 20 percent during lactation.
  • Reduced ratio of P1 animals to farrowing crates, allowing for a lactation period of 22 to 28 days.
  • Separation of P1 offspring for disease management and improved growth in nursery and finisher.
  • Reduced first weaning-to-breeding interval, therefore reducing the likelihood of a second-parity litter drop.

Natalie Knudsen Is a freelance writer from Mankato, Minn.