Whether purchasing replacement gilts or producing them in an internal gilt multiplication program, the goal is to begin with females that possess all of the phenotypic traits that result in a robust sow that will remain in the breeding herd for a long, productive life.
Research at Iowa State University (ISU) suggests that replacement gilts (purchased or raised) should remain productive for three to four parities to cover their cost in a farrow-to-finish or breed-to-wean operation.
When producers purchase replacement gilts, they entrust their genetic supplier to select for all of the production traits along with the phenotypic traits that influence sow productive lifetime. It is important to work with your genetic supplier to ensure that growth and backfat goals are met by every gilt.
Purchased gilts should be screened for reproductive as well as feet and leg soundness by the genetic supplier. On arrival, every gilt should be scrutinized to ensure all criteria are met. If gilts do not meet your criteria, work with the supplier to be compensated for the rejected animal(s). Generally, genetic suppliers do a good job of supplying quality replacement gilts. However, when gilt supplies are tight, selection criteria sometimes becomes a bit more lenient.
Regardless of source, all replacement gilts should be evaluated for feet and leg soundness, including size of feet, toe position, evenness of toes, joint angles and any injuries. Likewise, external maternal traits — genitalia and underline (teat) quality — must be scrutinized.
Reproductive Trait Screening
Modern maternal line females can easily average 14 pigs born alive per litter, so seven functional teats on each side of the underline is required; eight per side is preferred. Teats must be adequately spaced and correctly positioned so piglets can nurse unimpaired. Pin (underdeveloped) nipples and inverted teats are heritable traits and should be avoided.
Next, evaluate the size and position of external genitalia. A “normal” vulva should be sufficiently large so the gilt does not have difficulty farrowing her first litter. Infantile vulvas — those that appear extremely small — are often associated with an underdeveloped
Avoid selecting gilts that have an extremely tipped-up vulva. It is thought that a “tipped” vulva allows urine to backflow into the reproductive tract, which can contribute to cystitis.
Research has identified three feet and leg soundness traits that have a negative effect on sow longevity, and one trait that has a positive effect:
- Buck-kneed front legs. Gilts that have excessively straight front legs with a knee that buckles forward should be eliminated.
- Upright rear pasterns. When the angle of the hip, stifle and hock is too large, the animal is described as “post-legged” and should be culled.
- Swaying hind quarters. This trait is difficult to describe, but once you’ve observed a gilt with this tendency, you will remember it.
Typically, the gilt is long bodied and a bit narrow between front and rear legs. As the gilt walks away from you, her hips move excessively from side to side. These gilts exit the breeding herd more quickly that those with a more normal stride.
- Weak or “soft” pasterns. Of all feet and leg traits evaluated in several research projects, this trait appears to have a positive impact on sow productive lifetime.
There are several additional feet and leg traits that should be evaluated, although the scientific evidence of their importance is less apparent. They include:
- Foot size. Gilts should have a relatively large foot size with toes spread apart. This provides a greater surface area for the gilt’s weight to be distributed.
- Toe size. Toe size should be even. Research has demonstrated that toe size differences greater than ½ in. is a heritable trait. Uneven toes most often occur on the rear feet and are associated with overgrown heels and/or heel lesions on the larger toe. Overgrown heels and heel lesions occur because the larger of the two toes carries a disproportionate amount of the animal’s weight. Uneven toe size should be discriminated against.
- Cracks and injuries. Feet should be carefully examined for the presence of injuries, including cracks (white line, vertical wall, etc.). Gilts with foot injuries, cracks or other abnormal foot problems (i.e., overgrown heel) should be avoided because these problems tend to get worse as they get older. Some of these foot problems can be treated; however, it is often a costly, time-consuming process with no guarantee of success.
ISU research has reported that cull sows have a high prevalence of foot lesions. Sows with feet and leg problems are often uncomfortable while standing for any length of time, which may curb their lactation feed intake. Inadequate feed consumption forces the sow to draw on body reserves, which in turn affects her ability to produce milk for the piglets. As the demands on the sow’s body reserves become greater, her body condition declines, sometimes to the point where she is incapable of returning to estrus after weaning. Sows are often culled at this point for failure to cycle, while the real reason for this failure began with feet and leg problems that affected her feed intake during lactation.
In a recent project, ISU researchers studied rib shape and its association with sow longevity. In this study, gilts with a more barrel-shaped rib remained in the herd longer than gilts that were flat-ribbed. It is unclear why the barrel-shaped females performed longer, but researchers speculate it may be related to how sows got up and down while in gestation and farrowing crates and the development of shoulder lesions.
Focus on Soundness
One of the biggest challenges producers face is selecting and culling replacement females to ensure an adequate supply of gilts is readily available. Failure to adhere to high standards for reproductive and feet and leg soundness ultimately leads to higher culling and failure rates in the sow herd.
With proper training and experience, producers should be able to distinguish between sound and unsound replacement gilts. There is sufficient genetic variability for both feet and leg and reproductive soundness that selection should be effective at improving the traits, while decreasing the incidence of the undesirable traits.
Offspring from sires and dams that have undergone an effective feet and leg soundness evaluation should have fewer feet and leg problems, produce better and reduce the number of “downer” sows during transport and lairage.
The single biggest reason to improve leg soundness is to increase the productive lifetime of breeding herd females. This is important economically and for worker morale, as well as for the well-being of the females in the breeding herd.
Editor’s Note: A series of three production posters, “Conformation and Structural Soundness Guidelines for Replacement Gilts,” “Selecting for Feet & Leg Soundness in Replacement Gilts,” and “Selecting for Reproductive Trait Soundness in Replacement Gilts,” is posted at www.nationalhogfarmer.com. Print versions are available by calling the Pork Checkoff producer service line at 1-800-456-7675. (Request poster series #04842).