The objective of this study was to estimate leg soundness and body conformation trait variance using 1,449 gilts in a commercial sow unit. The gilts were from two commercial lines, the progeny of 58 sires and 836 dams. Sire information was not available for 52 animals.

Gilts ranged in weight from 249 to 297 lb. (273-lb. average) and in age from 183 to 197 days old (190-day average) when trait evaluation occurred.

Two experienced scorers, using a 9-point scale, independently evaluated all traits. Structural traits included six body traits – body size (length, depth, width) and body shape (rump shape, rib shape, top line) – and five leg traits per leg pair and leg action.

The degree in which the trait is controlled by the genetics of the animal (heritability) was estimated individually using available genetic software.

The model used to obtain the heritability estimates included (fixed effects):

  • Genetic line of the gilt (two genetic lines studied);
  • Evaluation day (to account for differences in the 14 individual groups of gilts delivered to the farm);
  • Scorer (to account for differences between the two scorers that evaluated all of the gilts).

The model also used “animal” as a random effect because each animal has a random sample of genes from each of its parents that contributes to its genetic make up.

All values were adjusted to a common weight.

Body size traits heritability estimates landed in the moderate range, between 0.20 and 0.32. Estimates for body shape traits were lower, ranging from 0.16 to 0.21.

Evaluation of leg traits – turned front legs, buck knees, foot size and uneven toes – had relatively low heritabilities (0.06-0.13). Turned rear legs, weak rear legs and both front and rear pastern postures had moderate heritabilities, ranging between 0.20-0.30. Leg action heritability was 0.10.

The relatively low heritabilities of some leg traits indicate that the proportion of additive genetic variance was small and genetic improvement through selection would likely be slow. The low heritability of leg action might be explained by the environmental factors contributing impaired movements, as well as the genetic influences. Some traits were considered moderately heritable.

Much as with many reproductive traits, genetic improvement through selection can still be made for traits with lower heritability estimates if sufficient genetic variance exists for the traits under selection.

Despite the relatively low heritability, further investigations regarding associations of soundness traits with reproductive performance and sow productive lifetime are warranted.

Researchers: M. Nikkilae, Kenneth Stalder, B. Mote, Max Rothschild, Anna Johnson, and Locke Karriker, DVM, Iowa State University, Ames, IA; Timo Serenius, Finnish Animal Breeding Association, Vantaa, Finland; Jay Lampe, Swine Graphics Enterprises, Webster City, IA; B. Thorn, Newsham Genetics, West Des Moines, IA. Contact Stalder by phone at 515-294-4683 or by e-mail: stalder@iastate.edu.